Though it means “exit,” the salida (steps 1-2) marks the beginning of the dance or movement. The caminada, or walk, requires the dancers to move through space for three beats. The dancing couple joins together during the trabada, with the leader marking the cruzada, or cross-step, for the follower. Beats six, seven, and eight are the resolución or ending.
There are 2 versions:
see the steps on edinburghtango.org.uk (http://www.edinburghtango.org.uk/tango/tangographics/basicstep.gif)
The name refers to counts in music, however, the man is not constrained to rigidly mark a step on each count or beat of the rhythm. He is free to hold or to syncopate, or cut the beat, as the music moves him or as space on the floor around him allows. The figure may be danced into or out of at various points and is not always entered at the beginning and there are shortcuts within the 8-count basic. For instance, the man may lead the lady from the cruzada at 5 directly to 2, or he may close his left foot to his right without weight on 7 and step side left directly to 2. So in actuality the positions which the dancers move through at each step are numbered as reference points.
(from tejastango.com (http://www.tejastango.com/terminology.html#8-count_basic))