"There is no celery in the fridge."
Translation:Tidak ada seledri di kulkas.
Ada is used to:
1) Indicate a location
Example: Tini ada di kantor = Tini is at the office
=> In this context ada is optionnal
2) Indicate a presence (means "there is" or "there are" in English)
Example: Ada kucing di dapur = There is a cat in the kitchen
=> In this case you need to use ada. => A more formal way is to use terdapat instead of ada
3) Indicate a possession:
Example: Dia tidak ada uang = He/She doesn't have money => In this case it is a synonym of punya, mempunya, memiliki
Adalah means "am, is, are" and is optional.
It is used to compare or describe two things which are the same or equal.
Dia adalah adik saya = she is my younger sister => "Dia" and "adik saya" are the same, so "adalah" can be used.