Warframe have a few different enemy factions, I will introduce you to the 4 most popular ones that you will constantly run into :)
Corpus are the high-tech enemies with tons of shields and are weak against Impact damage as well as Magnetic + Gas elemental combo.
The Grineer’s are heavily armored enemies which are weak against Puncture damage as well as Corrosive + heat/blast elemental combo (Some claim Radiation + Viral is good vs grineer – feel free to try it out, I think its personal preference and quite hard to distinguish between).
Infested are “squishy” (low/no armor – flesh) enemies and are very weak to Slash damage as well as Corrosive + Blast them as well this will literally melt the infested.
Void is a corrupted mix between corpus, grineer and infested enemy units and many people suggest corrosive + cold elemental combo against this, I think it’s hard to pick a side, I just always take something with high general damage – but in theory void enemies will scale and thereby increase in armor where corrosive is good, and the amount of shields they get can be weakened with cold damage.