The word Karma basically means action or actions. There are three kind of karma (karams)
1) The actions that we are currently.
2) The actions we did previously but we have not suffered the consequences of those karma yet.
3) The actions that we did previously and we have been ordained by Vaheguru to suffer those in this life.
Let's take an example of a bank account. Say prior to your birth in this life, you had total of 100 karma outstanding i.e. you haven't suffered consequence of 100 karma yet. At that point assume that Vaheguru ordained that since 100 karma are impossible to payoff in one lifetime, He decrees that you have to reap the fruits of 25 karma out of 100 karma.
The 25 karma that have been written on your forehead for this life cannot be changed and the gurbani pankitis like "Lekh naa matayee hay Sakhi, jo likhiya Kartaar" refer to these kind of karma (called Pralabhadh Karma).
The 75 karma outstanding and that have not been decreed by Vaheguru, are called Sanchit Karma and these karma are the first ones to burn when we do naam abhyaas. Pankitis like "Gur kaa shabad kaatay kot karam", (The shabad of Guru destroys tens of millions karma) pertain to these kind of karma.
The Pralabadh Karma (25 karma) cannot be erased but the effect of those karma can be minimized through baani. There are many saakhis to prove this. One of the saakhis is where Sooli (death by hanging) was changed to just a sool (small cut in foot) because of sangat of Guru Nanak Dev jee.
Based on our Pralabhad Karma (25 karma) we are put in situations and our reaction in those situations make up for our vartamaan karma i.e. the karma or actions that will determine our future.
For example, based on our Pralabadh karma (25 karma) say we become poor and have lot of debt. One is poor because of his or her karma but if because of the situation arising from Pralabadh karma, we start stealing or do other kind of sinful karma, then we will be building more bad karma. We don't have any control over Pralabadh karma but we have freewill on how we are going to react in this situation.
People talk about kismat, taqdeer or bhaag. Kismat, taqdeer or bhaag is nothing but our past karma. Our present condition is the direct reflection of our past karma. If one is rich, it is because of good karma in the past but most of the times, rich people end up in hell because where they become rich or king, they also commit a lot of sin. These bad karma done in the intoxication of authority or money leads them to hell. Our Tadbeer (present karma) shapes our future just as our past karma shaped our present. In reality all that we have is present. Past is a dream and future is also a dream. The past was enjoyed or suffered as present and the future will be enjoyed or suffered by us as present So really all that exists is this moment of present. Everything else is a dream.
Coming back to your question of suicide, say you are committing suicide because you have too much debt or you have been humiliated or raped. According to your karma you were supposed to suffer the aftermath of being under debt, leading post-rape traumatic life or leading a post-humiliation period of life. If you beat your karma and commit suicide, you did not complete the cycle of your karma. This way you will have to go through the whole thing over again i.e. you will be raped or humiliated or whatever over again. On top of this you will incur the very bad karma of ending your life i.e. depriving yourself of salvation and insulting the gift of Vaheguru i.e. human body. Furthermore, you will be mocked on in dargah. They are all going to make fun of you and how you ended your life based on false suffering because everything in the world is fake. Such person will have hard time getting human form of life again.
My advice to you is to do more naam and baani in this time. There is nothing that cannot be resolved by the power of naam and gurbani. If you have grave problem, I suggest you go to next amrit sinchaar program and plead for help. They will do ardaas for you (if they will) and then there is nothing in the world that can stop your Chardi Kala. I suggest you first speak to chardi kala walay 5 gurmukh elders in your community and then take the next step. One thing is for sure. Suicide is not a solution to anything. You will have to suffer everything all over again if you do so.
Gurmat is great and I am lowly person with lowly intelligence. It is quite possible that my writing up there contains serious misstatements about gurmat. Please let me know.
Daas, Kulbir Singh