Do you email the Landing Page to start a campaign?
Your campaign would start with a goal, (Ex. Landing Page), and connect to a sequence, that would contain the items that should happen after the goal is achieved, (Ex. Email Follow-up, Tagging ect)
Once this is set up, the lead would visit the landing page, and put in their information. The moment they hit submit, they will enter the campaign through the landing page goal.
I would like to share our Campaign Overview page from our help guide. There may be many useful tips and explanations about setting up campaigns, in this. http://help.infusionsoft.com/userguides/campaigns-and-broadcasts