As explained by other member, 이다 basically means "to be", while 있다 has a meaning of "to have" or "to exist". The two common form of conjugations (in present) for the two terms are, 이다 : 입니다　 ; 예요 / 이에요 있다 : 있습니다 ; 있어요 In terms of sentence structure, 이다 basically follows a noun to give rise of a meaning of "to be someone / something", e.g., 제 이름은 ABC입니다. = My name is ABC. 그녀는 주부예요/학생이에요. = She is a housewife/student. On the other hand, 있다 basically follows a subject particle, indicating a meaning of "someone / something is (exists)", e.g., 사람이 있어요. = People are here. / There are people. 열쇠가 있습니다. = I have keys. It should be well noticed that the negation form of 있다 is NOT 안 있다, but rather there is another specified verb, 없다. The two common form of conjugations (in present) for 없다 are 없습니다 and 없어요; e,g, 사람이 없어요. = No people are here. / There are not any people. 열쇠가 없습니다. = I do have the keys. === Good day. / 좋은 하루.

They are two different verbs and two of the most important, so it's good to get their meanings down right away. 이다 means "to be" in the sense of equivalence. 있다 means "to have" or "to exist" (the other meaning of "to be" in English). There's a lot more to know about these, but that's the basics.