zanést means the same as přinést and it has to do with Czech perfective and inperfective aspects.
lámat here means lámat kámen. i.e. quarry for stone
The sentence can be trasnlated: Ondřej brought lunch to his father, who was quarrying stone Underneath the Rock. (Pod Skalou here is a local name probably of a quarry, but it can be translated like this).: