Some , Any, A lot of

A lot, some, and any are used with indefinite amounts:
Example:
Q: How many students are there in the classroom:

A: There are a lot. (This is a large number). Or....
A: There are some students. (This is a small number but the number is not known.) Or....
A: There aren't any students. (This is zero or a very, very small number and the number is not known.

The "rules" that follow apply also to words containing some and any: somebody/anybody, something/anything, etc.
In general, some is used in positive sentences:
I got some nice presents for Christmas this year.
This job is going to take some time.
In general, any is used in negative sentences and questions:
I didn't get any nice presents for Christmas this year.
I looked in the cupboard but I couldn't find any biscuits.
I don't need any help.

In fact, the use of some/any is a little more complicated. Following are two common occasions when the above "rules" are "broken":
1. We can use some in questions when offering/requesting:
Would you like some more tea?
Could I have some milk, please?
Do you want something to eat?
2. We use any in positive sentences when we mean it doesn't matter which ..:
You can come and ask for my help any time.
Which book shall I read? - Any one. It's up to you.
You can sit anywhere but here. This is my seat!
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