Translation:What did you do yesterday?
Yes, the ます(masu) ending of a verb is for present and future tenses (there is no distinction between 'am doing' and 'will do'). To make it past tense ('did') then you change the verb ending to ました (mashita). So for example, 食べます is I eat/will eat, whilst 食べました is I ate; 買いますis I am buying/will buy, 買いました is I bought, etc.
Uh, apologies for the long grammar spiel coming up...
So in English, "did" and "was/were doing" are actually two different tenses.
The first is the simple past tense. It indicates an action in the past that happened and was over quickly, e.g., "the doorbell rang"
The second is known as the past progressive (or continuous) tense. It's generally used to indicate a past action that took place over a long period of time, e.g., "The cat was sleeping on the chair". (In English we also use it to describe actions that were in progress when something else happened, e.g. "I was eating dinner when the doorbell rang." Not sure if this one also happens in Japanese though).
Anyway, Japanese also distinguishes between these two tenses.
Past indicative (corresponds to simple past and past perfect in english): しました
Past progressive: していました