If you are using an iPhone/iPod/iPad, you touch the base letter (e.g. 'e') and hold it down. The possible foreign characters should pop up above the letter, and you can slide your finger (do not pick it up) to select the one you want.
If you are using an Android device, it is similar. You touch the base letter and hold it down. When the list of foreign characters appears, in this case you can lift your finger and touch the one you want.
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