I would like to connect to my home network when I am away from home. I have the GL-MT300N. Is this possible?
Yes, it is possible, but you would need to have an OpenVPN Server at your house and set the GL-MT300N up as an OpenVPN Client. The GL-MT300N by itself is not sufficient.
You need to decide what you want to do. Do you just want to pass your internet through the VPN, or do you also want file access to your home LAN.
The current GLi tools support routing for the client (TUN). If you want to surf the internet, send mail securely and get your Netflix from public WIFI then that may be all you need.
If you want access to the LAN resources then you may need bridging (TAP).
There is info for building a server on the OpenWrt wiki. Search OpenVPN. https://wiki.openwrt.org/
There is also relevant info on the OpenVPN site