Networking can be as simple as research which builds a network or collection of relationships. It is also building from one contact to another (and another), and maintaining relationships with them all throughout your career.
Identify a field or type of work that has captured your interest.
Gather early stage research on this field or type of work.
Identify and start a list of people who are working in your areas of interest.
Have a resume completed and reviewed before reaching out to contacts.
Reach out to ask if you can talk with the contact to learn more about his/her work.
When possible, meet in person in the contact's workplace.
Always thank your contact for his/her time and advice within 24 hours by email.
Nurture the relationship. Never burn bridges.