Maa (มา) has a few different uses — understand them by ear here. It puts the direction on the verb, coming this way rather than going away, which is why โทรมา is someone ringing you. On a verb of getting it means you went, got it and came back — ซื้อกล้วยมา is the whole errand. And after a stretch of time it reaches right up to the present: มาตลอด is “all along”, มาก่อน is “before now”.