I have a 1998 F150 with a automatic and it doesn't seem to get into Drive. The shift pointer need to point at "2" for me to go forward. If I point the shifter at "D" it is really in Neutral. But it feels like it's in 2 instead of Drive It has Overdrive and that seems to work. Also, when do I use Overdrive ?

Most likely the linkage between the lever and the gearbox is out of position. To fix it you must go beneath the truck to access the gearbox and this is a dirty work, better left to a shop.
An Overdrive is a device which is used in automobiles to allow the choice of an extra-high overall gear ratio for high-speed cruising, thus saving fuel, at the cost of less torque. Because of that it should be used only on highways, with the truck not fully loaded.