how do you check how many shards you have and whats the easiest way to get them?

[Keydah]

Shards are a tab in your inventory. The top of your inventory window has 6 tabs: 1, 2, 3, 4, shards, and key items.
The easiest way to get shards is mining and botany. They're a level 1 gathering item, so as long as you pick up miner or botanist, you can go to their nodes (check xivdb for where to find the nodes for each shard) and get them.

I don't know what level you need to be to meld materia, but it's pointless to do when you're leveling. You don't need them and you'll outlevel the gear you attach them to very quickly.