Welcome to the guild.

The rivers tutorial:
https://www.cartographersguild.com/s...ead.php?t=3822

Look at your hills and work out the direct route down the sides. Where water collects is where your rivers and streams will be. If they all collect up in a bunch you have a lake and it will exit out to the sea eventually. Rivers dont generally split so where it could pick the biggest and make that dominant and dry up the other exits.