For Windows:

Hold down the left ALT key and type the number code listed below using the number pad (right side of keyboard), then release the ALT key

If you are using a laptop, make sure the Num Lock is on, hold down the Fn and ALT keys and type the number code listed using the number keys in the middle of the keyboard; then release both the Fn and ALT keys.

Note that some characters allow more than one number code. Either number will work.

For Mac:

For Mac OS, in most cases, first hold down the OPTION key then a regular character key. Nothing will appear on your screen at this point. Release both keys, and then type the letter which should carry the diacritical. For some special characters press OPTION and one key together.