The volume we play music at is called the 'dynamics'. When you see the letter f like this:

It means play loudly (The f stands for forte is Italian for loud. It is a historical convention that most indications are given in Italian)

When you see a letter p like this:

It means play softly (p stands for piano, which is Italian for soft)

In most cases, you should continue playing at the same dynamic level until you see the next indication.

Try this piece. The tune repeats but the first two lines are marked 'forte' (loudly), and the second two lines and 'piano' (quiet).

Don't forget the dotted minim rhythm which stands for three beats:

Now try playing along with the accompaniment:

Here's a tune we've called 'The Bells' as it sounds a little bit like church bells ringing. Again, the same phrase is repeated, first forte (loud) then piano (soft)