SAI does not have text options. It's primarily a simple painting program so it doesn't offer text options, filters, etc. (most things that Photoshop would offer).
If you need text added to your comic, you'll need to use a program that has it like Photoshop, Clip Studio Paint, or GIMP. You can still draw your comic in SAI, but you'll either have to hand write your text (which is a viable option, lots of people do it, it's just a bit more time consuming), or save your file as a transferable format (I do .PSD for example, because you can open PSD in most functioning drawing programs) and move it to GIMP/Photoshop/Clip Studio Paint/whatever drawing software you can use that offers text tools and do so there.
I used to be in the same boat, I used Photoshop CS6 for my paneling, text, basically everything SAI couldn't do as well (if not at all). I've since moved to Clip Studio Paint and do most of my work there, save for some texturing that I still use SAI for
But that's just personal preference ^ ^"