I don't understand the differnces between these two properties.... I noted that if i insert for example col-md-5 in the first one in the html i can see this value..... If i insert it into the second one in the Html i can see it... But if i want to force this class into my object which is the correct one ?

.wBScolClass applies to the <div class="col…"> in which the current element lies (can be the element itself in some cases), in Bootstrap mode only.

.wCSSclassAdd always applies to the element itself, in all modes (classic and Bootstrap).