We use there is and there are in the present and there was and there were in the past. Depending on what's after these words, we will use different quantifiers. If you are having trouble with this, why not try these extra online exercises?
https://www.englisch-hilfen.de/en/exercises/confusing_words/some_any.htm
https://www.englisch-hilfen.de/en/exercises/confusing_words/much_many3.htm
https://www.englisch-hilfen.de/en/exercises/confusing_words/a_an_some.htm
https://www.englisch-hilfen.de/en/exercises/various/there_is_there_are5.htm