The secret is the Alt Gr (Alt Graphic) key.
In our case it’s just Alt Gr + E.
E.g. Alt Gr + ,/< will type “ç”.
Alt Gr combined,
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with letter keys types accented letters.
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with symbol keys types either the rest of the symbols depicted on the key or other special characters.
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with the horizontal numeric keys or some symbol keys types a pending accent that will be placed on the next letter you’ll type if the combination exists.
You can also use
Shift + Alt Gr + key
for capitalisation of characters or for even more special characters.
Memorising those combinations you’ll rarely need to change the keyboard layout or deploy more complicated ways to insert special characters in text editors, just test it on your keyboard and note down the important combinations or those that you can’t remember easily.