If your source file is correctly encoded as UTF-8, you can simple write "société". Basicly you can use any character you would ever want, when you use UTF-8 encoding.
But, if you for some reason don't use UTF-8, but use for instance ASCII encoding, you are forced to write é This is a very good reason to check you are using UTF-8 encoding in all your source files.
Where you need to use html entities is for instance:
- & which is written &
- < which is written <
- > which is written >
But remember it depends on, where in the html code. In attribute values, you also need to replace:
- " with "
This is what I remember of the top of my head. But use a html validator, it will tell you, if you have problems of this kind.