Once you have created a GEDMatch account, you can upload one or more autosomal DNA files. This will allow you to match against the GEDMatch database and use GEDMatch's tools.
Before you begin, you will need to have a copy of your raw results from a DNA testing company on your computer.
Go to the GEDMatch page. Login by entering your email and password and clicking the Log in button.
Click on the Generic Upload FAST link in the Raw DNA file Uploads area on the right.
Fill out the form with information for the person who tested and whose file you are uploading.
Note, if this is not you, you should ask the person tested's permission before uploading their data to any 3rd party website.
Select the data file you are uploading from your computer.
Wait for the file to process. Do not leave the page until you see the completion message and the ID at the bottom of the screen.