If Buddhists believe that life is just suffering why don't they just kill themselves?

Buddhism does not "teach life is suffering". In the 1st noble truth, Buddhism teaches "attachment to life is suffering".

This said, Buddhism does teach life is essentially worthless & meaningless (SN 22.95). That is why it is reported in the scriptures that many monks did end their life after seeing its worthless nature.

However, if life is truly seen as meaningless then it is so meaningless that one would not ever bother to kill themselves.

Before say such, just notice this Buddha never said that everything thing in this life is makes us suffer and of course there are things makes happy, joy, pleasant feelings. but soon as we feel them we get suffer being loose it. As you say by taking our own life wont save us, wont solve any problem, instead it creates more problems.

why don't they just kill themselves?

ha..ha....ha....

If Buddhists believe that life is just suffering why don't they just kill themselves? What does the Buddha say?

This is a common misunderstanding of Buddhism. While it's correct that Buddhism teaches that conditioned reality is marked by suffering, it also teaches a way to end suffering.

The answers you are looking for can be found in the teaching on The Four Noble Truths, namely The Noble Eightfold Path.

You were getting a lot of short answers -- I don't know whether they were meaningful to you (because I don't know how much you already understand or know about Buddhism).

If Buddhists believe that life is just suffering

I think that Buddhists don't believe that.

There's doctrine about parents' love for their children, for example -- that's not just suffering.

There's doctrine about cause-and-effect -- which says that some actions (or some intentions) lead to suffering (and are therefore unwise, unskillful, and tainted) -- and some actions don't (and so are skillful, virtuous, and "right").

Perhaps the fundamental doctrine of Buddhism is the "four noble truths" -- here is a simple translation (SN 56.11):

1. "Now this, monks, is the noble truth of stress: Birth is stressful, aging is stressful, death is stressful; sorrow, lamentation, pain, distress, & despair are stressful; association with the unbeloved is stressful, separation from the loved is stressful, not getting what is wanted is stressful. In short, the five clinging-aggregates are stressful.

2. "And this, monks, is the noble truth of the origination of stress: the craving that makes for further becoming — accompanied by passion & delight, relishing now here & now there — i.e., craving for sensual pleasure, craving for becoming, craving for non-becoming.

3. "And this, monks, is the noble truth of the cessation of stress: the remainderless fading & cessation, renunciation, relinquishment, release, & letting go of that very craving.

4. "And this, monks, is the noble truth of the way of practice leading to the cessation of stress: precisely this Noble Eightfold Path — right view, right resolve, right speech, right action, right livelihood, right effort, right mindfulness, right concentration.

There are topics on this site (e.g. here or here, see also here) which point out that the Buddha didn't say "life is stressful".

If I paraphrase the first noble truth (quoted above) then the (finite) list of what is stressful includes:

• Birth, ageing, and death
• Unhappiness and despair
• Being with (associating with) what you don't love
• Losing (separation from) what you love
• Not getting what you want
• "Clinging" (upādāna) also translated "attachment"

The second noble truth is that this stress is caused by "craving" -- for sensual pleasure, craving for "becoming" (i.e. to become something), craving for "cessation".

The third is that when craving ceases, so does suffering.

The fourth is that the Buddhist "noble eightfold way" is the path or practice which leads to that cessation.

why don't they just kill themselves?

Well "death" is stressful, killing is stressful, and so on.

It's not what the noble truths say.

A lot of Buddhists profess a doctrine of rebirth -- and use that doctrine to argue against suicide ("no point in killing yourself -- you'll just be reborn, maybe worse off than before") -- I think I've even some use the same argument as you, to explain the doctrine of rebirth, i.e. "rebirth is why you wouldn't just kill yourself".

This topic -- Secular Buddhism and Suicide -- has answers or explanations which don't depend on a doctrine of rebirth (I think that "secular" Buddhism is a form of Buddhism, especially in the West, which ignores or is agnostic about various traditional doctrines that might be understood as supernatural, including any doctrine of rebirth).

By existing you are attached to this reality

Given that you also wrote this statement I might add that another important part of the Buddhist doctrine is the doctrine on anatta or non-self.

A lot of your statements or thinking includes, for example, "I exist" or "I won't exist" and so on.

An introduction to the anatta doctrine might be here -- Anatta-lakkhana Sutta (SN 22.59):

"So, bhikkhus any kind of form whatever, whether past, future or presently arisen, whether gross or subtle, whether in oneself or external, whether inferior or superior, whether far or near, must with right understanding how it is, be regarded thus: 'This is not mine, this is not I, this is not myself.'

It's not easy to understand perhaps (there are 100s of topics tagged anatta on this site), but may be fundamental. A clear explanation is maybe How is it wrong to believe that a self exists, or that it doesn't?

I think this answer was based on the first and maybe second suttas of the Pali canon -- but see also How to explain what Buddhism is? for more comprehensive descriptions.

If suicide would have been a solution then Buddha would have said so. Buddha would have said there is no need of Dhamma, just go and kill yourself. Craving doesnt end upon comitting suicide.If craving doesnt end then the person who commits suicide will take rebirth again in good or bad realms. If you can commit suicide without any craving then you will attain Nirvana. But craving can not end without ending greed, anger and delusion. Therefore one should focus on ending greed, anger and delusion rather than on ending life.

Buddhists do kill themselves, but instead of killing the body they kill the Ego -- which is much more effective.