Whether it be for five people or five hundred people, wedding invitations should reflect on the creativity and personal style of the couple being wed. They can be very expensive, or inexpensively made; the real point of the wedding invitation is not how cute the card can be, but whether the wedding information is properly conveyed to direct guests to the right location at the right time on the right day.
The invitations can be as simple as an email with a nice background, or homemade on card stock. They can include glitter and paint, or be printed professionally on elegant paper with script and decoration. Invitations can be delivered in person, as well; as long as guests know how to RSVP to the invite, the choices are infinite.
With the information included on the invite should be how to respond to the invitation, what time and date the wedding will be taking place, and if there are any gift requests or clothing preferences. The wedding invitation might also specify any other personal information the couple might choose, like where the reception will be, or the honeymoon.
As with a lot of decisions made in a new marriage, reflecting on personal choices as a couple is an important step in the right direction, and there's no better place to try out joint decisions and creativity than with a wedding invitation. The sentiment will be one to treasure for years to come, and will be a beautiful reminder of the day that two people joined their individual lives into one.