Learn German: Er ist auch da. - He is also there.

In this sentence it translates to "he" and likely refers to a person. However, in German, er is also used to replace any masculine noun (words that use der). So if you were talking about der Tisch (the table), you would also use er to say "it" is also there.

Why do we use ist here instead of bin?

ist is the form of the verb sein (to be) that matches third-person singular subjects like er (he), sie (she), or es (it). If the sentence started with ich (I), you would use bin (ich bin auch da).

Does da always mean "there"?

While it translates to "there" in this sentence, da is very flexible. It often just means "present" or "around." For example, if someone asks if you have arrived at a location, you can say Ich bin da to mean "I am here."

Could I change the word order to "Er auch ist da"?

No, you cannot do that in German. In a standard statement, the verb (here, ist) has a strict rule: it must be the second idea in the sentence. So, Er takes position one, ist takes position two, and the extra detail auch has to come after the verb.