I need to type the Euro symbol
AltGr+ 4 or 5 or E (varies with the keyboard layout).
MAC: ⌥ Option+3.
Add Answer is reserved for solutions. If you think the answer is not satisfactory, add a comment below, or click edit (below your question) to add more information. Thanks.
Check the mark (
→ 
) to the left of the answer that solves your question.
You can replace AltGr+ with Ctrl+Alt+.
It amuses me to see how a simple question triggers so many answers. 
It’s a great team.
This only proves that the answer is easy and that asker could have found it if s/he took the time to look for it locally in his/her computer help. But with internet and Q&A or forums, laziness encourages to get precooked solutions instead of learning by oneself. And this may take longer that a personal research!
This is usually best done with your OS and is not LO-specific. You didn’t mention it nor your locale, so my answer is only a hint.
Depending on the keyboard and font associated with it, a common binding is Alt Gr+E.
To show the community your question has been answered, click the ✓ next to the correct answer, and “upvote” by clicking on the ^ arrow of any helpful answers. These are the mechanisms for communicating the quality of the Q&A on this site. Thanks!
In case you need clarification, edit your question (not an answer which is reserved for solutions) or comment the relevant answer.
For Mac user: Shift + Option + 2
For Windows user: Ctrl + Alt + 5
Hello,
since you asked on LibreOffice site here is the method supported by the application:
Type U+20AC immediately followed by ALT+X (or ALT+C in some locales)
Everything else is a matter of operating system, keyboard layouts and other mappings (e.g. shortcuts)