so I have a canon 6D jst being wasted as I'm not using it much so I was thinking I'm about to start a YouTube channel so I was thinking is it possible for me to record my self while I'm gaming like those youtubers who do that??
or do I have to buy webcam??
If you only plan on 15-20 min tops before taking a 15min break, sure, as long as you have the proper capture equipment (better to capture from HDMI output). Anything longer than that and you need a webcam or camcorder
15-20 mins would be more than enough..
can I know what equipment do I need to do it???
Live or pre-recorded? If pre-recorded, just click record and you're done. After that use your favorite video editor to overlay. If live, you'll probably need to get a dedicated capture card (something like elgato HD60) and then whatever broadcaster you normally use.
If all this is above your head, you need to search around the twitch FAQs and other places until you understand the terminology and performance impacts you'll see.