Panel:SetTooltip
Example
Give DButton a tooltip, that will be automatically shown when the player hovers over the button for a certain amount of time, decided by tooltip_delay
ConVar.
Output: 

Sets the tooltip to be displayed when a player hovers over the panel object with their cursor.
By default, DTooltip will be used. Panel:SetTooltipPanelOverride can be used to override the tooltip panel.
Give DButton a tooltip, that will be automatically shown when the player hovers over the button for a certain amount of time, decided by tooltip_delay
ConVar.