The English word “bank” can mean a financial bank or the side of a river:
• “She deposited money at the bank” points to a financial bank.
• “They sat on the river bank” points to the river's side.
The word first has more than one possible meaning. The rest of the sentence provides a clue, so one meaning is selected.
This is only an everyday model of the reasoning. In Usul al-Fiqh, Ta'wil requires reliable evidence and qualified scholarly analysis, not a learner's guess.