Pawpaw seeds need a 6-8 month stratification. This can be achieved by planting them in the fall in a coldframe or outside, in pots or situ. Or, you can put the seeds in the refrigerator in a plastic bag with some moist peat moss. It is very important to keep the seeds moist- if they dry out they will lose their viability. I have had good success this season with the fridge method, my tray of 38 has had a high germination rate..although it takes a couple months for them to show themselves as they grow a deep taproot before any aboveground growth. Supposedly Pawpaw seedlings prefer partial shade in their adolescent stage- I have not verified this with experience.
If you want a quicker fix then buy a grafted Pawpaw tree. For superior cultivars with larger fruit and more flesh/less seeds, check out the work of Neal Peterson. Happy Pawpaw growing