Best data model to do if we have various data sources?

Hi experts,

I would like to know, what is the best data model that we can do if we have various data sources.

For example, currently i have 3 Excel where all three have no unique values. What i did was i merge and append them together in one table.

But i find it's not the best solution because somehow the table is heavy so the performance is quite slow.

Should i create the unique ID and try to relate them by ID or how ya? And should i create the dimension table as well?

I'm so confused right now.. HELPPPPP!

Your help is much appreciated.

Thanks,

Nurul