If you are talking about Battleforce see page 213 in SO. It describes a BF Element as being the same as a TW Unit.
Elements are formed into BF Units (Lances, or Stars in the Clan organisation) that move around the map. If using AS then the Units remain individual Mechs, CVs, CI platoons.
If BF, see page 225 for combat description where each Element in a BF Unit gets to make its attack(s), take damage, Critical Hits and so on.
Page 239 has a force distribution table where a Clan Star (Unit) has 5 Elements, IS Lance, 4 Elements and ComStar Level II, 6 Elements.
See the example on page 240 for building a Unit. The second column describes forming Clan Stars.