Dear Friends,
This may sound a little weird, instead of doing the opposite I have to move from tables to ER diagrams...
I have already created the tables (relations) for my DB, but now I have to present them in ER model, unfortunately I am struggling at this phase.
I need some tips and tricks about how to convert from tables to ER diagrams.
What should I take care, the constraints, how should I treat them?

My tables are created in Excel and also in Microsoft SQL, but I don't know how to move from relational design to ER design.
After understanding this I will also need a good software for drawing the ER, what do you prefer me, it has to be something stylish.

Thanks in advance