If you mean posting on your own website. First you need to get a host provider which will give you domain name and storage space, after you make the account you login into the c-panel provided by the host and you upload your game files there using FTP server, you can use the built in tool or filezila.
If you are talking on other websites, like kongregate or armorgames. You need to create an account and there is upload options where you can put your game. On armorgames first you need to request an developer account, on kong you can upload right away.
Edit: I am using https://byet.host for my personal hosting services, they have free and premium plan. Usually the free one will get the job done unless you plan getting more then 5000 visits a day.