The Seed Exchange

Hello! Obviously I'm new here (I think we all are). Does anyone have advise on self-pollinating (should I cover some blossoms and pollinate them myself)? I'm just getting more into gardening and started everything from seed this year. I used mostly heirloom seeds and would love to save enough seeds for myself next year, to share with my local library, and to share with people here. I do have many varieties growing next to each other and open pollinated. I don't want to give anyone seeds that don't produce the same thing next year. I had a volunteer zucchini crossed with pumpkin plant last year and want to make sure I'm not sending something like that anywhere.