I cant figure it out
You have four kinds of troopers (at least I've encountered four kinds so far). Normal weapon, can be one rifle or two pistols, nothing special. With a radiating antenna, has a handset and can command troops with it. Rocket launcher, can destroy anything that needs explosives, these targets are silver. Machine gun, can destroy anything that needs constant fire, these targets are gold.
Not to forget, in the huge battles you can use the normal troops to destroy golden objects, too. Just take your clone with the handset, bring him close to a full platoon of normal clones and use the handset. You will see a line from the commander to his soldiers, they will follow him. Now target whatever you want to attack and send them on their way. They will even get reinforcements, if necessary.
For the ground battles, you may want to get the Super Speeders red brick, it'll allow the little speederbikes to destroy all buildings.. it's a little slower for the gold ones. You can also use the RX-200 tank for Republic or Homing Spider Droid for CIS.. their beam weapons slice through gold buildings quickly.
Both of the methods posted by The_6th_Beatle work; a third way is to use the Force to take control of a Super Battle Droid and point the droid at the gold object to make him blow it up for you.