Money is any object in which you can exchange for goods or services. We consider this currency. Money is also a store of value so that you can get those goods and services at a later time (so you don't have to immediately use up the currency right away if you don't need to).
If at some future date, the unit of money isn't able to purchase as much as it used to, then we say that inflation has occurred. For example, if a loaf of bread costs $1 today but then $5 ten years from now, then we say inflation has kicked in.
-------------------------
Before we talk about M2, it helps to start with M0. That's a zero and not the letter 'oh'. In economics, M0 is the total collection of all cash (bills and coins) that are in circulation. This means we're just talking about physical things people can touch. Building to M1, it involves everything M0 talks about plus things like travelers checks and demand deposits. So if you're talking about M1, then you involve all physical cash as well.
Then finally moving to M2, it involves everything M0 and M1 does, plus savings accounts and time deposits. By "time deposits", I mean things like mutual funds and money market accounts. Basically things you may hear about when talking about wall street.
In short, M2 involves all physical cash plus other electronic stores of value (this is a fairly vague definition but it may work in many settings). It does not involve large time deposits as that is what M3 handles.
