Confused

This is my second month trying to use YNAB. Here’s where I’m struggling…

I get paid once/month on the last business day. My August 31 check actually deposited on Saturday (August 29), though didn’t actually show up in my RTA until last night (with an August 29 deposit date, so I’m not sure why it took so long to show up in RTA. It showed as an inflow right away)

In my mind, I’m using that money in my September budget, though I think I’m understanding that I should assign it in August and then the amounts not spent (almost all of it) will just roll into September.

So - I assigned my check in August, and then when I change to September it says I am negative in RTA.

I think I also may be confusing targets and assignments. Are they the same thing?

Also - full disclosure, I am a jump-into it type of person, I haven’t sat and watched the getting started guide. Maybe that would clear things up?

Hope all this makes sense. Thank you!