It's very simple. After you must have typed the codes, let's say on a notepad application then you'll choose 'save as'. After getting to the save tab, in the name box, let's say you are naming your save file as index, you'll append the HTML extension to it e.g 'index.htm' or 'index.html'. Afterwards you'll change the file type to 'all or something suggesting that' and you may go on to save.
After you have completed the above you can now open the html file with any web browser. Although, there are some advance editors capable to write with and also used for test running purpose. However, one step at a time; as time goes on, you'll learn about other tools and how you can use browsers like firefox and chrome to your advantage.