It sounds like OP doesn't know wtf vector and raster are, so here's the basics.
Raster is a grid that represents the pixels on your computer screen. It's the final product, basically.
Vector art is a set of instructions. Draw a line from here to there using this color. The computer then paints it on your screen.
The great advantage of vector art is that you can upscale it. If you try to make a raster bigger, you end up with big blocks. So if you're working in raster, start with a big canvas size. You can always scale it down if you want the final image to be smaller.
So work in whatever your favorite art program uses. Save your work files on your computer in your art program's format, and export it to raster format (jpg usually, webp is getting more popular) for sharing online.