This is a geminate root: the second and third letters are the same מ, so it often looks like just two letters at work. One idea runs through all of it: heat. From it you get the bare adjective חַם (hot), the abstract noun חֹם (heat itself), the verb that makes things warm, the place where you keep things warm (a greenhouse), and even the sun as the hot one. Notice how the niqqud and the doubled מ shift the same three consonants from quality, to substance, to action, to place. Every word here is verified against pealim, niqqud included.
The same root runs through the verb system. Each binyan is a voice: it bends the one idea into active, passive, causative or reciprocal. Tap to hear.
In everyday Hebrew the verb of this root lives almost entirely in the active pi'el לְחַמֵּם. Its natural partners exist too: the passive pu'al (to be heated) and the reflexive hitpa'el לְהִתְחַמֵּם (to warm oneself up, to warm up before sport), whose action-noun הִתְחַמְּמוּת appears below. The plain pa'al is not lexicalized for this root.
Same root letters, different noun moulds (mishkalim). The mould tells you the function: who does it, the act of doing it, or the thing produced.
Strip the prefixes, suffixes and vowels. Three consonants remain, and the meaning lives there.