Have a look at your keyboard. Now locate the following keys: é, ö, ü.
Still looking? That's because they aren't there (well they are, but we'll get to that), just like several other useful keys we'd probably use a lot more if they were actually visible.
To get these symbols into your writing as I've done above all you need to do is familiarise yourself with Alt Keys.
By holding down the Alt key and pressing a sequence of numbers on the number pad (note: you have to use the number pad on the right of your keyboard and not the row of numbers along the top) you can use several special characters that are otherwise not available.
Here are the most common:
é = Alt+130
É = Alt+144
ê = Alt+136
Ê = Alt+0202
ö = Alt+148
Ö = Alt+153
ô = Alt+147
Ô = Alt+0212
ü = Alt+129
Ü = Alt+154
± = Alt+0177
© = Alt+0169
™ = Alt+0153
½ = Alt+0189
This is technically how you produce these characters on your computer, however, what I usually do is find the symbol with a simple Google search, copy the character and then paste it wherever I need it to go.
Simple as that.
The choice is yours.