I am trying to figure out what is the difference between "ist" and "es"? for example in the phrase "Mein Auto ist blau" vs. "Mir geht es gut", can you say "Mir geht ist gut"?
"Ist" is 3rd person present tense of the verb "sein", English translation "to be (He, She, or It is)".
"Es" is the 3rd person singular personal pronoun, English translation "it".
There is no situation where you could use "ist" instead of "es". Therefore, "Mir geht ist gut" is not correct, maybe you misheard.
In the first sentence, "Mein Auto ist blau," ist is the form of the verb "to be" that corresponds to "is," which links Mein Auto (the nominative)l, and blau, the predicate adjective. "My auto IS blue."
In the second sentence, "Mir geht es gut", GEHT is the verb, and "gut" is the predicate adjective. "Mir" is the indirect object, and es (it) is the nominative. A literal translation of the sentence would be, "To me goes IT well." or "IT'S going well with me."
If you've studied Latin or Spanish, it's easy to confuse the two, because in those languages, "es" is a form of the verb "to be," just as "ist" is in German.
But in German, the two are different word forms and therefore never interchangeable.