When is a good time to plant......

I am a new gardener. Never was good at it growing up, but thought I would give it a try now that I am older.
Now I am wondering what I should be planting.
I planted a few different types of tomato that failed miserably. But the ones I put in my topsy turvy are producing fine.
My okra is beautiful. But my squash, bell peppers, and eggplant are withered or still not producing.
When is a good time to plant these?
And also, when is a good time to plant potatoes? Carrots? Turnips?
I'm trying to understand the almanac, but, it's a hard read!
Any help would be appreciated.

Mary :-}