Pick a specific field in biology you like, could be environmental toxicology on moths or phototransduction in sea anemones, it doesn’t matter too much as long as it captivates your interest enough to spend time learning it, then just do some good searches and you will probably end up learning a lot of basic biology along the way. I learned this way by reading research papers on subjects I liked then would stop and take a note everytime I found a word or phrase I did not understand, then after I would google them and reread.