I just got a yearling red eared slider and he won't eat yet so I was wondering if you could give me some advice
Red-eared sliders need a balanced diet. Give him commercially sold pellets (ReptoMin is recommended) and feeder animals, such as crickets.
Young turtles are mostly carnivorous; their protein intake is important. My brother fed Fred mealworms, crickets, spiders, and other treats.
However, they do need nutrients from pellets in order for their shells to properly develop, depending on how much sunlight they get.
As your turtle matures, also supplement his diet with fresh (organic) vegetables.
Young turtles need to eat daily; older ones (such as Fred) may skip a day. At the same time, do not overfeed your turtle.
Also, turtles are messy eaters. It’s good if your buddy can eat the pellets whole. Some sites recommend having a second tank for feeding.