The first step is to create an account at https://avatarrelics.com/my-account/. You can either log in with your Twitch/Google account or create an account directly. Once your account is created, make sure to connect to your Twitch/Google at https://avatarrelics.com/my-account/social-accounts/.
Once your account is connected to the streaming platform, you can convert viewing time there to Gems here.
If the steamer has gold or other chat currency, you can run !goldconvert $amount to convert some of that chat currency to gems here. In general, 10,000 chat gold will convert to 1 Avatar Relics Gem.
If the streamer has Twitch Channel Points setup, you can redeem some of those points to convert them to Avatar Relics Gems. Again, the standard conversion rate is 10,000 Channel points to 1 Avatar Relics Gem. There may also be rare badges that can only be unlocked for large amounts of Channel Points that, in turn, unlock rare items here.