You don't really help in the question...
Which OS do you use?
Linux based OSes usually are using a centralised spell checker for almost all of the application that you use inside the OS.
Windows on the other hand doesn't have this kind of tool, and you have to download it for each application you use. If Firefox for example, you go to the add-ons and type the dicos you need in the search and install it from there (for firefox just type add-ons in the adress bar, it will connect directly to the main site).
The spell checkers from the official are often quite good, but you also doesn't say which is your native languages.
The choises is really up to you.
You don't really help in the question...
Which OS do you use?
Linux based OSes usually are using a centralised spell checker for almost all of the application that you use inside the OS.
Windows on the other hand doesn't have this kind of tool, and you have to download it for each application you use. If Firefox for example, you go to the add-ons and type the dicos you need in the search and install it from there (for firefox just type add-ons in the adress bar, it will connect directly to the main site).
The spell checkers from the official are often quite good, but you also doesn't say which is your native languages.
The choises is really up to you.