As a new player, the best cards to collect from dimension rifts are Loki, Groot, Star Lord. Get each of them to 4* with good stats then start building 5* options until you get one with good stats and replace, etc.
Mythic uniforms in legendary battles and a CTP selector from getting Mythic Pymtron which should be used on one of the premium CTPs that you can’t get for free. You get a CTP of Energy for completing the story. CTP of Refinement from Giant Boss RAID if you get lucky. You can also get them from buying chests but don’t do that.