Although your camera won’t make any adjustment to the exposure when you’re working in Manual mode, it provides useful guides.
The histogram is a good place to start. With the Iive histogram displayed on the rear screen (or in the electronic viewfinder of a mirrorless EOS camera), you’ll be able to monitor the effect that the aperture, shutter speed and ISO are having on the overall exposure as you make the changes. For example, as you can see in the histograms shown here, you can shift the histogram to the left and make the picture darker by using a lower ISO and/or a faster shutter speed and/or a higher f-number than the setting that’s currently dialled in. Do the opposite if you want to make the picture brighter.