Start out by logging into your facebook account or create one if you do not already have one.
Upload the photos that you wish to tag your friends in. Make sure that the friends that you wish to tag in the photos all have facebook accounts as well because you will only be able to tag people that are your friends on facebook.
Click the button under your profile picture that says View Photos of Me. This will bring you to a page with all of your facebook photo albums on it. Click on the album with the picture that you would like to tag.
Click on a picture that you would like to tag your friends in. Scroll down to the bottom of the page and click the button that says Tag This Photo.
Click on the area of the picture that your friend is on and a small box will appear. Scroll through this box for your friend or start typing their name in the box. Once you find your friend that you would like to tag in your photo, click on their name and then click Tag.
Your facebook friend will get a notification telling them that they have been tagged in your photo. Your friends can also tag photos that you have uploaded to your facebook account.
You can repeat this process as many times as necessary for all of the pictures that you have on your facebook profile.