Push is a newbie offensive skill. Most players that get it will soon get access to something better, but it is far better than nothing. Rangers have a guild task that requires using push, and even have access to a guild boon to make it useful for disrupting monster skills. Still, this is fundamentally a newbie skill and not used much past the lower levels.
The ingame help reads:
Skill duration: 2. Type of skill : offensive skill. Party rows : 1st. Affecting stats: Str. It uses 11 endurance points. While fighting an opponent in a melee, there are many ways a skilled attack can gain an advantage. One of the simplest forms of fighting taught, is to step into the target and give him a solid shove. While the damage is light, this skill is easily mastered and the basis for many fighting styles. The stronger the fighter, the harder he can push his opponent.