I realize I made this tiny tutorial (to practice making tutorials) a while ago and I can't believe I never shared it here. (It's a gif, so if you don't see it moving, you might need to refresh?)
Obviously, there's a ton of ways to make bubbles, but my thinking when I do it this way is: it doesn't require any special tools outside of copy, pasting, flipping, and having layers-- which are all very basic features to just about ANY digital art program! So, it's a nice and easy way to start making bubbles by hand or if you don't have any advanced tools in whatever program you're using.
It also allows you to make the speech bubble more square than circle! Most blocks of text are going to be square-ish because that's the nature of text blocks, so this can allow you to more easily fit your dialogue.
So, hey! Maybe it'll help you out. Feel free to share the way you make your speech bubbles down below, if you like.