Hello and welcome to the forum. If his fins are clear in some spots then it means new growth. Since you've only had him for a few days then I wouldn't worry too much about him not eating unless he's pale and laying on the bottom. Not eating for a few days is pretty common with new fish as they get used to their new surroundings. You can post any questions you have in the diseases and emergencies section of the forum.
hello im new to this but i have a betta in need. His name is Yin and i dont know what is wrong with him. he is a half moon betta that is red and blue. I got him 4 days ago and all he has eaten is possibly one betta pellet. I got some freeze dried blood worms but he is not eating them either. i am also concerned because the end of his fins are going clear and this black gills are portruding from their places. Please help!