OBS supports different encoders if the corresponding technical requirements are met. Note: Never pass on your stream key and change it immediately if you accidentally showed it to the public! You should copy it from your Twitch Dashboard and paste it in OBS on this page.
Besides that, you need your stream key for Twitch which you can find on Twitch on your Dashboard > Settings.
Most of the time there are several servers that can be used, so you should test them and find out what works best for you. First select the platform of your choice from the list and then choose the closest possible server.
