The 2016 free agency period gets started with a "soft opening" on Monday with the opening of the "tampering" period. Starting at 9 a.m. PT, teams are allowed to speak with agents for players and work on contracts. Deals cannot be signed until 1 p.m. PT on Wednesday, but some deals will be effectively completed before Wednesday.
The NFL has made some changes this year to remove some of the ridiculous nature of the tampering period. Previously, teams could exchange positions, but there could be no formal offers and no agreements in principle. That obviously was happening anyway, and so the NFL has issued a memo with some adjustments to the rules.