when one leaves a bathroom and before davening, one needs to wash. i see many people using a cup, while in mishnah brurah it seemed that the times we need to use a cup are limited to other events. am i missing something?
There is a difference between washing after the bathroom, and washing before davening.
According to the strict halachah, there is no need for using a cup, or for washing three times, after entering and after using the bathroom. It is sufficient to clean one’s hands with water (Shulchan Aruch 165:1; Eliyah Rabbah 4:12; Rosh Kelal 4, no. 1; among others).
However, some authorities, such as the Chida, mention that it is good to wash three times after leaving the bathroom. Yet, even according to these authorities there is certainly no need to use a cup (see Minchas Yitzchak 5:96, who cites a number of sources on this question).
For washing before davening, however, some rule that one needs a proper netilah (similar to before eating), which is with a cup (this is the opinion of the Rambam Berachos 6:2, and a number of rishonim as cited by the Beis Yosef 4:7).