If your computer is really laggy, there is a built in screen recorder for windows 10 at least, maybe other windows. This can't capture more than one program, but is good if you want non-laggy runs
I use windows 10, did you say this program is built in or do I have to install, it?
Also, do you know if I have to stream on twitch to submit minecraft speedruns?
Windows has it's own built in recorder, but I would avoid using it unless absolutely necessary as it has some limitations.
All questions regarding a specific need to be directed to the mods and community of the game; every game has it's own requirements for acceptable proof of a run (although I've never heard of a game requiring a live-stream).
@SpeedSonic if you don't have the built in recorder I would suggest downloading OBS. Its free and the best screen recorder for speedrunning. If you can't get OBS, then bandicam or screencast are also good.