A guide to creating a basic soundfont in Polyphone, step-by-step:
1: Make a new soundfont.
2: Drag your samples into the left side of the screen under "Samples". If they're tonal samples and/or are labeled by note, they should have their key values assigned automatically. If not, go to Tuning and assign this value manually.
2.5: Assign loop points if your WAV files didn't come with them already. The toolbox has a feature to quickly set loop points.
3: Click the sample up top, then click the sample at the bottom, then click the speaker icon. ("New Instrument"
4: Assign key ranges, velocity ranges, and volume envelope ADSR. Once you're done with that, then click the instrument and the note icon.
5: Make the new instrument preset.
Additional tips:
Don't forget about the toolbox icon, it has a bunch of useful utilities that make instrument creation easier. For example, if you assigned your samples before tuning them, sample auto-positioning can fully automate the process of building key splits.