A few things to remember:
If you are talking about your camera setting, sRGB/aRGB only affects in-camera JPG. If you shoot raw, it does not apply.
If you shoot aRGB but have a narrow gamut monitor, you will see false colors as your software tries to map the larger set of hues to a more constrained display. If you want to use aRGB or really see raw colors, you should get a wide gamut monitor. diglloyd.com has some good articles about this. Many of the newer Apple products have a wide-gamut display now, or there are the dedicated ones from many companies. I use a Benq 2700, which I got refurbished from them here in the states for a good price. There's a few things you want to consider, such as how it can be calibrated (and yes, you should also get a calibration device to keep it tuned up). See diglloyd.com articles.
As the previous poster mentioned, for on-line display you must use sRGB as that is what everyone can view and the colors will look wrong to people if you use aRGB, at least for what you export and post. For prints, especially fine art or metallic prints (which I really love!), exporting to aRGB as per your print shop requirements will give you better prints.
So, just to make it clear, raw files have the max color gamut of the camera, and aRGB comes in second, then sRGB. In your photo editing software, you will work in some color space (e.g. sRGB, aRGB, ProPhoto RGB), which could be wider or narrower than the original file (hopefully not narrower). It will try to render the colors as best it can from that color space onto your monitor, but your monitor might not be able to show them accurately. When you are ready to export your photo, you can select what color space to use for the export. For on-line, that is pretty much always sRGB. For print, it is usually aRGB (assuming the original was at least aRGB and the editing was at least aRGB).
Another helpful article is
https://photographylife.com/srgb-vs-adobe-rgb-vs-prophoto-rgb
Marc