My Work

I work at (1) in a hospital as an administrator of a  in logistics center where (2) which provides only medical supplies goods for group groups of hospitals which are serving more than 30 places.  

私は病院で働いており、30以上ものグループ病院へ医療材料を提供する物流で管理者として働いています。

Hi Sachiko,

Just some suggestions for your writing:

(1) We work in our workplace. "At" expresses a location, and "in" expresses an enclosed space or a building, which is our workplace. 

(2) We use "which" to focus on an aspect (i.e provides only medical supplies...) of something that you have previous mentioned (i.e logistics center). In your sentence, you were trying to focus on the services provided by the logistics center that you work in. This is why we use "which".

We use "where" to provide more information about a situation.

Example: 

There have been cases (situation) where (not which) temperature excursions have taken place when our trucks were transporting sensitive medical supplies (provide more information about a situation).  

I hope this helps.

My job

I work at in a hospital as an administrator in of a logistics center, where which  provides only medical supplies goods for  to group hospitals hospital groups which are. These groups are in more than 30 places.  

私は病院で働いており、30以上ものグループ病院へ医療材料を提供する物流で管理者として働いています

Hello! You should take into consideration that in English language the sentences should be written shorter than longer. So try to create simple sentences and it would be better for you :)