If you are unsure of your plans, you might say "I might go to Paris". In other words, you haven't made a decision. You might go and you might not go. If there's a good chance that you're going to Paris, but it isn't yet certain that you will/can go, you could say "I might be going to Paris". For example, someone has invited you to Paris, you want to go, but it depends on whether you can come up with enough money to buy an airline ticket. Similarly, you could say "I might be going to the Ed Sheeran concert" if a friend has offered you a ticket, but you have to get out of another commitment before you can accept. Despite what I've just said, in these cases it would also be perfectly correct to say "I might go to Paris" and "I might go to the Ed Sheeran concert". To me, this is not an issue of grammar, but a matter of tone. "I might be going" suggests expectation, whereas "I might go" is neutral. Here's someone using "I might go" to be deliberately neutral/mysterious: Tom: I might go to Paris. Bill: Really? Tom: I'm thinking about it. Bill: Where are you going to get the airfare? Tom: Maybe that's not a problem. Bill: Not a problem? ... OK, time to stop being mysterious. Spill the beans. What's happening? Tom: My girlfriend bought tickets! We're going to Paris!

Grammar is uncountable. It doesn't have a plural.

In the scenario I thought of in my head: I might go to the grocery store later. I might be going to the grocery store later. To me, these have the same meaning. Does the book provide any other information?