The people you invite or invite you. When you “accept” to form a connection with someone you form a first level relationship with them in your LinkedIn network.
A second degree connection means it is a friend of a friend, you are separated by two degrees. Three degrees away is someone you can read through a friend of a friend and one of their connections.
This is where you can check personal messages sent to you by other LinkedIn members.
Introductions are requests made to other LinkedIn members that you do not have a direct connection with. It is as it sounds, a way to introduce yourself to someone you do not necessarily know. LinkedIn limits the number of introductions you can have pending at one time.
This is what you send when you ask someone to connect with you. You invite them to join your network.
Groups are exactly as they sound. They are groups of other LinkedIn users. Groups can be used as discussions or forums for people to connect or get advice and job postings.
Your network is the group of your connections, you are the center of your network. It can also include the connections of your connections.
This is the page you control. It holds your picture and credentials. You have the ability to post job history and upload a resume. This is what others see when they click on your link.
This is a request you can send out to have another LinkedIn member. If they agree, they will then write a short paragraph recommending you. This is visible to anyone who views your profile.