What does "use bitcoin" and "use sats" mean to you?

If you are asking about what others use bitcoin for, ... that varies from person to person. I might use it mainly for remittance payments, for example, where I use Strike to send funds to another country. Technically, bitcoin was used in that but when I used Strike, only dollars from my USD balance with Strike were used (as far as me the user of the app is concerned).

Others use bitcoin for buying things -- especially things that are not sold for anything but bitcoin, or those purchases in which bitcoin makes the checkout process easier, or better protects your privacy.

And even a greater number of people "use bitcoin" to earn. How? Usually by speculating ... by either trying to time the market (i.e., buy low, sell high), or by "dollar cost averaging" (DCA) (i.e., repeated bitcoin purchases for a certain amount (in USD), at certain periodic intervals ... such as weekly). In doing DCA purchases, over the long term (e.g., multiple years), the hope is that the value of the bitcoin purchased will be greater than the amount of USDs used to make those purchases. Another way people try to earn is doing tasks and stuff, ... even like what you did by asking your question here on SN (from which you earn some tips). Bitcoin mining is another way people earn bitcoin, but that requires a significant investment in the bitcoin mining hardware, so that's generally not something a person new to bitcoin should just dive into.

Some people use bitcoin for their business -- accepting payments from customers in bitcoin. There are many methods for doing that. Even for something like a musician, like a DJ that produces samples -- maybe Wavlake is a good app to take a look at.

The bitcoin ecosystem, being permissionless, and global, is very large. So for you to obtain better answers to your question, perhaps could you share what brought you here, or what your interests are?