If you want to try saving seed, beans and squash make it easy to get started. After the main harvest is over, let the plants dry with the remaining pods. If necessary, bring the plants in under cover to finish drying in Fall. The pods are easy to thresh when they are very dry. Don't save seed from moldy pods.
Squash are easy and fun to work with.
Just tape shut female blossoms the night before they will open. The next morning, collect some male blossoms and use them to hand-pollinate the female blossoms. Replace the tape on the female blossoms after hand pollinating. You can tell which are the male blossoms because they sit atop long stalks. Successfully pollinated fruits will develop while those that are not pollinated will shrivel.