Your question is really broad and instead of a plain a precise answer, this should be a series of questions. Not enough information to give you just -one- answer. Let's try.
Unless your previously configured your RPI O/S, it is not trivial to work without a monitor, also, will be convenient to have a UART to USB cable plugged to GPIO 6/8/10 and use Putty to talk through the 'console', however, not having them is not the end.
You did not mention your RPI model, nor the O/S your are trying to use, I must add that you can't start with the default NOOBS distribution: you will need interaction (and a monitor)
Now, the following is the most basic and generic setting for a headless unit, also works with Zero:
- Download the latest Wheezy or Jessie image from the Raspberry PI site
- Extract the image from the zip file
- Use win32DiskImager to create a new SD card
- Install the memory card on the device
- Connect your Ethernet cable.
- Connect the power micro USB.
You will need to find the DHCP assigned IP address then fire your Putty SSH connection.