M odern EOS cameras have a number of features and functions to help you to focus manually. Mirrorless models are better equipped in this department, but EOS DSLRs also include some useful indicators.
For a start, there’s the focus indicator. Select a single AF point, point it at the detail you want to focus on, and the circular focus indicator at the bottom of the viewfinder display will illuminate once the area covered by the AF point is into focus. The AF point itself will also blink red.
Switch to Live View mode, and you’ll be able to take advantage of the magnified rear display to check that small details are in focus. Repeatedly press the magnifying glass button to blow up the area covered by the focus square: from x5 to x10 zoom, returning to the full (x1) image again.