Nothing magic about sending strings, or having functions that does it for you.

But you have two choices.

Functions that sends one character at a time, waiting for the UART to be ready for the next character. Polled is "old-time" and affects the timing of your program, but has the advantage that it doesn't require any buffer memory.

Functions that sends the data into a buffer and quickly returns, while the ISR picks up data from the buffer. However, buffers have limited size, so the function either have to fail if the buffer can't accept more, or hang and wait until there is room for more data. This is especially important if you use printf() or similar to print strings that are larger than the buffer size, i.e. even if you check the remaining space in the buffer before the call, the buffer can't hold a single string in full.