Hi, If you have the money to spare and you are really dedicated to art, it might be a good investment. If you are just doing art for fun, you can get GIMP for free. [link] It's similar to Photoshop but doesn't have as many features.
You can download a free trial of photoshop if you want to try it out.
The makers of GIMP made a questionable choice to make the "save" function save files in gimp format. Probably because the gimp format will automatically retain all of the options, layers and settings that are available in your file.
However you can EXPORT the image as a PNG, JPG etc. using the "export" function.
Photoshop is the de facto standard for most non-vectorial art. You'll be able to do a huge amount of things including digital painting and photomanipulation.
You might hesitate with PaintTool SAI though - it's a specialized-for-digital-painting tool and is more ergonomic than Photoshop (as in, more beginner/intermediate user friendly). On the other hand it doesn't do anything else than that, whereas Photoshop is polyvalent.
also I think if the person you're talking to can differentiate between vector and raster, there's a good chance they also know those words...and if they don't, you know, they can just google what you said. if you start saying stuff like "non-vectorial", well, how are they going to google that?