You will start to receive friend requests once you start posting updates, participating in groups and commenting on the activity of others.
When you have a new friend request, you will see a notification, as shown below.
Simply click on the notification and the list of all notification will appear. When you click on one friend request you will be taken to all friend requests, with each shown as a block like below with the profile image and name.
Click on the Actions icon and the options to Accept or Reject will appear. Click on your choice.
If you choose Accept, your new friend is now added to your friends list.