There are a few ways you can still recover things here.
First, Do you have something on the drive which you need to recover? If you do, you'll need to find a friend with a Mac that you can connect your Mac to using Target Mode (see below on how), then using a file recovery program try to recover your files. Whats important here is if you try to restore your OS before salvaging your files there is a likelihood you'll damage some of them.
OK, let say you've got a good backup or don't care whats on the system lets move on ...
If you have a means to connect to the internet (Ethernet connection) and your systems firmware has Internet recovery services you should be able to recover that way. Here's a good writeup that explains things: How to Re-Install OS X with Internet Recovery on a Mac. Beware! this process will take quite awhile. Start it up and spend the day or night doing something come back in 8 or so hours things should be ready for you to continue. Make sure your system is plugged in as well.
OK, you don't have a good internet connection (very slow) or none at all. Then you'll need to find a friend with a Mac which you can either connect your system to, or you can create a USB thumb drive recovery disk (16 GB or larger). You'll need to connect your system to your friends via a FireWire or Thunderbolt cable in Target Mode. Here's a good write-up: How to Boot a Mac in Target Disk Mode Basically, your system becomes an external drive to your friends Mac allowing you to install the OS onto it.
If you can't use Target Mode then you'll need to setup a USB thumb drive as a bootable drive and then copy the OS installer to it. Here's the steps for that: How to Create an OS-X El Capitan Boot Installer USB Flash Drive