(something/anything) in particular

"In particular" means "specifically" or "especially". If you want "something in particular", it means that there's one specific thing that you want.

So, for example, if you're talking about food, there's a difference between these sentences:

I don't want anything.

I don't want anything in particular.

The first means that you're not hungry. The second one means that you don't have one specific kind of food that you want.

(someone) is in the mood for (something)

A "mood" is a temporary feeling that you have, which normally lasts a few hours. For example:

Don't talk to her now. She's in a bad mood.

In this example, you're saying someone has been angry or upset for a few hours or for a day or two.

When you say "I'm in the mood for ___", it really just means "I want ___". But saying you're "in the mood for" it makes it sound like it's a temporary feeling. This works well when you're talking about food, because you want different food on different days, depending on how hungry you are and what you've eaten recently:

I'm in the mood for something light.

is there (something)(clause)

Here are some examples of this construction:

Is there a day when we could meet and discuss this in depth?

Is there a certain size you're looking for?

Is there something you wanted to tell me?

Use this when you want to ask about whether a certain kind of person, thing, or idea exists.

In the example at top, you're not sure whether your friend is in the mood for a certain kind of food. And you don't want to make your friend decide where to go. You just want to be polite by checking to see if he has a strong preference first. Asking "Is there anything in particular...?" will give your friend the freedom to choose what he wants to eat, or to let you pick something if he doesn't care.