The Player Trade Status screen (Team Menu >> Transaction section >> Player Trade Status) is where you can manage the trade statuses of players on the selected team:

The Player Trade Status sub-screen behaves very similarly to the Overview page, except that by default the bottom transaction boxes default to player trade status boxes. As with the Overview page, to make a transaction, drag a player from one pane to another, or right-click on a player and select a transaction from the right-click menu.

This screen is described in more detail in the section of the manual on trading

See Roster Rules and Management for more information on transactions involving waivers and DFA.