For an even better start with C2, I'd suggest you to go also over the Beginner's guide for C2.
Just to clarify, Construct2, once a license bought, comes with 124 sounds.
For the free version, the free bundle only contains 16 sounds.
But yes, you can use any of your own sounds and as many as you want, as long as the computer's performances allow it.
Be sure to read the manual entry about sounds and music.
In C2 you will have to use the audio object.
A word of warning though, audio support in HTML5 is "fragile".
Nevertheless, as you said C2 helps a great deal in making games and the community is there in case you need it.