Here's a collection of some resources that you might find useful for learning about various topics.
- General undergrad physics and intro quantum field theory: David Tong's lecture notes
- Cosmological inflation: Daniel Baumann's Cambridge lecture notes, Leonardo Senatore's TASI lectures
- Cosmic microwave background: Martin Bucher's lecture notes
- Large-scale structure: Anthony Challinor's Cambridge lecture notes
- Galaxy lensing: Martin Kilbinger's review article
- The cosmological constant problem: Cliff Burgess's Les Houches lecture notes
- Statistics: PDG review article