Mass Effect Legendary Edition

A burst/combo is performed by using a tech ability on an enemy while another tech ability is already affecting them or a biotic power while another biotic power is already affecting them.

You can combine with squadmates for the burst/combo (or use 2 squadmate abilities for it)

I was playing a tech build character that had both Overload and Incinerate. When they are highly upgraded, they would both last long enough for my 200% cooldown speed (for only equipping pistols) to finish. So i would Incinerate and enemy, wait for cooldown, then Overload. When you use it, a big explosion should happen on them. That's a burst.

Biotics can be really easy to get a combo too. Using something like Singularity can leave a target open to be combo'ed upon for a few seconds. I would recommend finishing it off with a Warp personally. The fun thing is that you get someone with both Singularity and Warp as a squadmate before you even get control of the Normandy.

A quick way to grind this with an Adept Shepard:

In the game's first minutes you're given the tutorial to shoot, ignore the instructions and use Pull and Throw at them until it times out.

Soon after you'll have a very long fight after you trigger the radio in a downed gunship. The battle is scripted so the enemies just keep on coming, until you run out of ammo or time it out and get saved in the last minute. Don't shoot at the enemies, just Pull and Throw them. You'll progress both, this and Sky High at the same time.