Insert and Retrieve data at same time

Question

Hello,

We are doing backup/restore functionality on base of one Entity. so let's say system is doing restore for Entity 1 (which is 1 million rows), now at the same time User's of Entity 2 needs to Retrieve or insert a data in the same table.

Note: Table can contains rows of multiple Entity.

I want to implement something so that if one or more Entity is doing Restoring functionality other Entity Users don't have any problem for fetching or inserting a data into the database.

I have read about Isolation Level in database but dont have clear idea about it.

thanks,

Piyush