Not trying to self-promote, but I have about 100 pages of basic category theory notes I was planning on eventually pushing towards internal/two-dimensional category theory and putting on the arxiv as a survey article. They've been sitting around for two years now, though, so I uploaded them in their current (very unfinished) form in case they might help you. All the content on $1$-category theory is solid (sections 1-7), and sections 8-9 are serviceable, but please ignore the later sections for now.

They assume no familiarity with anything besides what a set and function are, although being familiar with the naturals/integers/rationals as distinct entities will help understand an early example of a non-surjective epimorphism. If you need to develop familiarity with sets please feel free to grab any standard text on set theory and read it, or if you like my notes you can try this arxiv paper I uploaded a few years back which builds up the set theory you'll need from scratch. Again, the research at the end is shaky and shouldn't be used, but pages 1-6 give a 'from-scratch' development of the axioms of MK class theory and the stuff through page 19 offers some basic lemmas to try and prove (don't read my proofs unless you need to!)

Best of luck, and remember not to beat yourself up if things get challenging! The level of abstraction in either of the above note sets is likely to be a signifigant step up from the kinds of mathematics you've encountered thus far, so be sure to come back to MSE and ask further questions! (MO is a bit too high level for this stuff generally speaking, as evidenced by the users trying to close the question, but these are completely reasonable questions over at MSE)

Not trying to self-promote, but I have about 100 pages of basic category theory notes I was planning on eventually pushing towards internal/two-dimensional category theory and putting on the arxiv as a survey article. They've been sitting around for two years now, though, so I uploaded them in their current (very unfinished) form in case they might help you. All the content on $1$-category theory is solid (sections 1-7), and sections 8-9 are serviceable, but please ignore the later sections for now.

They assume no familiarity with anything besides what a set and function are, although being familiar with the naturals/integers/rationals as distinct entities will help understand an early example of a non-surjective epimorphism. If you need to develop familiarity with sets please feel free to grab any standard text on set theory and read it, or if you like my notes you can try this arxiv paper I uploaded a few years back which builds up the set theory you'll need from scratch. Again, the research at the end is shaky and shouldn't be used, but pages 1-6 give a 'from-scratch' development of the axioms of MK class theory and the stuff through page 19 offers some basic lemmas to try and prove (don't read my proofs unless you need to!)

Best of luck, and remember not to beat yourself up if things get challenging! The level of abstraction in either of the above note sets is likely to be a signifigant step up from the kinds of mathematics you've encountered thus far, so be sure to come back to MSE and ask further questions! (MO is a bit too high level for this stuff generally speaking, as evidenced by the users trying to close the question, but these are completely reasonable questions over at MSE)