This is another case where the wiki can help.
In
the article about Bombards there are all kinds of basic tips on their behavior, weaponry, drops, etc. But look to the panel to the right under
Statistics and you'll see a breakdown of this unit's weaknesses and strengths, with a bunch of damage type icons and (+) and (-) to show what damage is extra effective against them and which they resist.
In the case of Bombards they have
Alloy armor, which is strong against Slash, Electrical and Magnetic damage, but weak to Puncture, Cold and especially Radiation damage. Underneath that armor the Grineer are
Cloned Flesh, strong against Impact and Gas damage, but weak to Slash, Heat and especially Viral. To the extent you can choose weapons with mods that attack Alloy and Cloned Flesh best, you'll find these particular enemies becoming less and less a problem for you.
In the early going you may not have access to the weapons with some of these elemental damage types, nor the mods you use to add these damage types to your weapons*. So from the get-go its enough to know the basics: That against Grineer, because they are armored, Puncture damage is most effective. Against Corpus, you want Impact and Cold to take down their shields, and against Infested you want Slash and Heat because they are fleshy monstrosities. Check your weapons and mods to see what you have best to bring in against each faction. As your arsenal expands and as particular enemies annoy you, look them up in the wiki and see if you can optimize your builds to take them down quickly.
* You can either slot base damage type mods like Cold, Heat, etc, or create combined effects by slotting multiple distinct damage types that work together to produce more complicated elemental damage types like Corrosive, Radiation etc. Just slotting these mods will increase your weapon damage, but combine them with a high status % and you'll not only do the elemental damage in terms of raw numbers, but also "proc" the effect of that type: When Heat damage procs, enemies will be set on fire and flee, Cold procs freeze enemies, Corrosive procs will literally melt enemy armor, etc. This system has a ton of depth to it and can be found in detail in
the Damage 2.0 article. Once you understand Damage 2.0 you'll know how to be super effective against enemies in the game.
Its a lot to take in at first, and can take a while to come to grips with, but once you do the whole nature of the game comes into view.
