All quotes from Wookipedia:
Skywalker was skilled in the use of telekinesis able to lift heavy objects with minimal effort. During his duel with Asajj Ventress on Yavin IV, he easily deflected a large pillar back at Ventress when she hurled it at him and immediately afterwards he used the Force to block her Force Push without even slowing down. He was also skilled at Force Jump, and was able to leap massive distances. Skywalker was also capable of a powerful Force Push; however it should be noted that despite having a stronger connection to the Force than Obi-Wan Kenobi, his Force Push was unable to overcome Kenobi's during their duel on Mustafar. He was also skilled at Jedi Mind Tricks. However, Skywalker also had a habit of using the Force Choke power, a sign of who and what he would later become.
Because his limbs were severed and his body severely burned on Mustafar Darth Vader lost much of his Force potential. As Darth Vader, Skywalker was believed to have had roughly eight-tenths of the strength of the Emperor. But even still, Vader wielded tremendous power and skill. Had he sustained none of his injuries on Mustafar, he would have been even more powerful than the Emperor.
Because of his decreased mobility, he was at a disadvantage when dueling against beings using faster and quicker combat styles like Ataru. To counter fast-moving opponents, he would use the Force to pull out anything from his surroundings that wasn't nailed to the ground and fling the improvised missiles at his opponent. Without moving a muscle, anything from the venue of the battle could be used as a weapon to crash against Vader's opponents from all directions in a never-ending barrage. Darth Vader first used this tactic in the Duel on Mustafar, slicing shards of metal from the walls and shooting them at Obi-Wan Kenobi. Darth Vader also used this tactic to bring down Jedi Knight Roan Shryne, and most famously Luke Skywalker in their first duel on Bespin.
It should be noted that Darth Vader, despite being a powerful Sith Lord, was unable to generate Force lightning. This was due to his cybernetic implants, and any attempt by Vader to generate it would cause it to backfire, electrocuting his life-support systems, causing it to short-circuit and kill him.
Vader also appeared to have great physical strength, able to lift a grown man by the throat with one hand, and picking up the Emperor and hurling him to his death. Whether these feats result from his use of the Force or from the power of his cybernetic limbs is unknown. However, it seems most likely to be a result of his mechanical appendages, as when he choked Kenobi in their battle on Mustafar.