A closer look
Present tense is the verb form for what is true now, what happens regularly, or what someone feels. Past tense is the verb form for what already happened. I jumped in the lake. I was happy.
Present tense covers more than right now. It also handles habits and states, so I work in a library describes an ongoing fact, not this exact moment.
Past tense is not the same as the perfect forms
Present tense is not the same as past tense. I walk to school is present tense, describing something happening now or something you usually do. I ate lunch and I jumped in the lake are past tense, placing the action before now. Past tense also covers states: I was happy means the happiness belonged to an earlier time.