What do you apply before foundation?

What base products do you all use before applying foundation?

I usually apply foundation right after sunscreen, but lately I've noticed a lot of people using tone-up bases or primers separately. I'm curious if using a base definitely helps makeup apply better or if it provides better tone correction.

And I'm also confused about how much base product to use.

If you apply too much, it feels like it's rubbing off,

Also, if I apply too little, the tone correction doesn't work.

I feel like it's fine in the morning, but by the afternoon, it feels like there is almost no tone correction effect.