If your entry door is stuck, first examine the entire door to discover which points are sticking. If the door is rubbing against the door jamb by the hinges, place cardboard shims behind the hinges and try the door again.
The next elements to examine are the hinges themselves. The screws often loosen over time, making the plates come undone and causing the door to shift slightly out of place. Tighten the screws to secure the plates on both sides of the hinge. You may need to replace the screws with longer ones if the anchor has given way, causing the shorter screws to continually lose hold.
If the problem is not fixed at the hinges, use a power or hand planer to plane the door where it sticks. Set the planer to 1/32 inch to remove a minute amount of the edge until it opens and closes easily again. Make multiple passes if necessary, but be careful not to create a gap that does not seal when closed.
Finally, look carefully at the strike plate and latch to gauge if it is too far away to catch. Create a new mortise with pilot holes and replace the strike or use wood putty to partly fill in the old mortise hole.