I've just recently started with video capture so others here will probs have better suggestions however if you have nVidia then you should have something called shadowplay.
If like me you have Radeon (amd or ati) then i use MSI Afterburner. I installed the Lagarith Lossless Codec and that seems to give acceptable results.
You can either have a key-combo setup so that you can manually start/stop record, or you can set it to automatically record (then overwrite) the last X minutes of action and by pressing a key-combo save that buffer to disk.
Either way, after that you will need to video edit your work, at the moment i just use Windows Movie Maker which give good but basic features.
Once complete you will need a Youtube account and channel to post your work on.
Have fun
