Spells, Psionics, and Magic Crap
In 3.PF, magic is the undisputed king of battlefield control and debuffs. From the old classics (the Wall line of spells, Grease, etc) to spells like solid fog, resilient sphere, and forcecage, spellcasters of most stripes excel at locking down sections of the battlefield and defining the engagement on their terms. Mass debuffs like sound burst or color spray can take groups of enemies out of the fight temporarily or permanently.
Forced movement is more rare and the only examples I can really think of are all from 3.5, not Pathfinder (though your DM might allow you to port them - check the Spell Compendium). Hindering movement, on the other hand, is everywhere. Look at spells like slow or transmute rock to mud, and mass lockdowns like black tentacles.
And the non-magical stuff...
Is sadly, for the most part, garbage. Attacks of opportunity, trips, and bull rushes are 100% of the control options available to non-casting characters and their utility is sadly limited. Attacks of opportunity don't do enough to discourage creatures to stay out of your space; trips require large amounts of investment and taper off rapidly due to the average size of monstrous enemies increasing rapidly. Bull rushes are less useful than trips to begin with and suffer from the same flaw of enemy scaling, with the added pain that you're giving up damage to do them. Avoid it if you can, but if someone's really dedicated they can pick up a reach weapon, some method of boosting their size, and Combat Reflexes to get the start of a melee 'control' build. Just understand that it's not really going to happen in a game that emphasizes non-humanoid enemies.
3.PF has no aggro mechanic, and the one feat to that effect (Antagonize) is aggressively and insultingly poor and should not be considered for control use under any circumstances. However, you can approach this problem from the other side through the use of spells like charm monster, suggestion, dominate person, and the like - they convert a monster into an ally for a nice length of time, making it fight for you rather than against you. You can also attempt to make a given target more attractive by having that person attack a monster's weaknesses - for example, a fire elemental may preferentially assault someone doing cold damage (against which it is weak). However, this approach has no hard mechanical backing and is dependent on DM interpretation.
Low-Level Specific Tricks
Having just read that your question is interested in some low-level options, here's a few to help you through levels 1-5 or so.
Items - Tanglefoot bags and nets are the big famous low-level options that can lock down individual opponents. If your DM lets you port in 3.5 content, check out marbles too for a hilarious way to deny sections of the battlefield to your enemies on the cheap. Melee characters interested in control will want to look into a weapon that grants them reach.
Spells - Color Spray, Grease, Cause Fear, Daze, Sleep, and Charm Person are control staples in first level spells. Look for spells that can lock down or get rid of large groups of enemies at once (see Sound Burst), or that can impede mobility (like Entangle).
Feats - Welcome to the only time period in which Attacks of Opportunity are a threat all on their own. Check out Combat Reflexes as a feat, and consider investing in tripping if the game is going to stay low-level, though this is the most feat-intensive option (requiring Combat Expertise, Combat Reflexes, and Improved Trip at a bare minimum).