You can purchase memberships for yourself, as well as for others, where creators have enabled this option. Read more about how buying a gift membership works here.
Some membership plans include guest access. You will know if guest memberships are included in a plan if you see the following note: "[number] guest memberships"
This means that, as a member, you can give guest access to as many people as specified in the plan. They can then use your membership for free.
You can manage these guest accounts under Memberships. They remain active until you cancel them or your own membership expires. Read more about setting up and managing guest accounts.