RE: how do I set specific price for a product and store combination ?
Hy Saravanan,
pricing in D365 Commerce/Retail can be impressive.
Basically for easy processes you create one Price group for all channels or as many price groups you want to serve with different prices.
Each channel could have his own price group or all channels can have the same price group.
The price group has to be connected to the channel, which means it is handled as a trade agreement for that price group that is connected to a channel.
As Price groups can be of different types (discounts, affiliations, loyality, ...) it can get confusing.

For further setup of retail pricing it is essential to understand the concept for the retail pricing mechanism
https://docs.microsoft.com/en-us/dynamics365/commerce/price-management#price-groups
As said before for an easy setup of sales prices it works to create a new price group at Retail and commerce/pricing and discounts/Price groups/all price groups
Create a new price group, and create a new trade agreement for that group with the sales prices you need.an post it.
After that you go to the retail stores, navigation menu "Store", then Action pane "Pricing", "Price group", assign the previous created price group. Of course aö price need to be distributed before they are available at the stores.
Good luck.