Light tanks have little armor, a less powerful gun, but they are usally very fast. These tanks can be seen in the BT series, which are very, very fast and have the speed to quickly get across flat terrain. These would probably not be in the direct front of battle.
Medium tanks are almost the perfect combination of speed, firepower, and mobility. Keep in mind it is almost. Certain tanks would have more armor than other mediums, some faster, some with larger guns. These tanks were mostly used in WW2
Heavy tanks are heavy. They have heavy armor and a large gun, at the cost of speed. Lots of heavy tanks would go at 14 KM/h, which is pretty slow compared to the 30 and 50 KM/h acheived from medium and light tanks. The heavy can take many hits before they get destroyed, so they would be in the direct line of fire.
There are 2 types of SPGs, Modern, and Older. The modern SPGs are fast, with little armor but a gun that could pack a punch. Some are called self propelled artillery, but those are different. Old SPGs were slow, with a big gun and even thicker than some heavy tanks armor. These guns could destroy enemy tanks or encampments fromm miles, which was why they were developed.
Self Propelled Artillery usally is slower, but has HUGE guns. These guys sometimes have 150mm guns, thick armor, but like older SPGs, they are slow. They usally have 150mm guns, which are big enough to put a tank down from a distance, and they sometimes are used for their name, as artillery.
SPAA is a weird one. These are semi fast, but they have light armor and small guns. Their guns do fire super fast, which is why they are used for anti-aircraft reasons. They can cut down aircraft with ease.
These guys are just SPAAs, but they have missiles. They can be used for shooting down other missiles, shooting down slow or low-flying planes, or just used against tanks if they need to. The missiles could easily shoot down enemy helicopters as well.
The MBT is the perfection of the Iron Triangle. They have great armor, a great gun, and good speed as well. They are seen in the T-90 and M1A2 "Abrams". They can easily take out enemies from a long range, and they can relocate if they are seen with ease. They could be seen as the perfection of tanks. These are more modern than the other tank types and will probably be used for a long time.