I rescued these plants from dumpster but don't know what they are?

definatly a juniper species. it may be a rug type that are low growing groung cover type plants. i have a "blue rug" juniper and they make great cascade style bonsai. they are very hardy and like full sun

I'd say Juniperus communis 'Repanda'.

how should i go about using them eventually for becoming a bonsai

let them be for now if they were thrown in a dumpster they need a little time to recover.they are quite overgrown at the moment so some hard prunning will need to be done once healthy to create some shape...this leaves some time to research the species and figure out how you may like to design them cascage,upright,raft styles come to mind

Thank you for all the help