Adding animation to current project results in t-pose

Hey all,
So I have been trying to learn UE4 for the past 3 days and I have to admit it’s really really fun so far! I have however, run into few problems and I’ve looked at tutorials online but cant seem to find this particular issue anywhere. Ill ask my question this way:
Say I downloaded from the market place basically blue print of attack, jump, and some other random action. Say I then used this as my main character, however, this one doesn’t come with block animation. I then download block animation from mixamo website. I believe you have to download a skeletal mesh first before importing the animations because it’ll simply wont work. Ok now I want to add the block animation that I downloaded from mixamo to my current work- could I do that? Even though the block animation came with a different skeletal can I still take animations and add them to my work?
This engine is really really confusing, most of the tutorial is from 2017-18 and the layout of the newer version has changed. I still don’t know where skeletal re-target is located?
The biggest hurdle is finding the retarget option because a lot of youtube fix issues that I am currently facing anytime I import anything using retarget but I cant find it anywhere in my current version running at 4.26.2.