You want to connect your company's internal network using a Windows Phone 8.1 smartphone? This procedure explains how to setup a VPN (Virtual Private Network) profile on your device:
Create your VPN profile
Go to Settings > General > VPN and toggle VPN Status switch On. The next step is to set up your VPN profile.
Tap on the + button to create a new profile. Fill in the following information (most of the information will be provided by your admin):
Server name or IP address is the VPN host name or IP.
Type refers to the protocol being used (IKE, IKE2, SSL...)
Connect using allows you to choose the connection method (username+ password)
Enter your username and password, and that's it.
Configure your settings
You can leave the Connect Automatically switch on, if you want your device to automatically connect to the VPN when required.
Leaving the Send All Traffic on will transmit all the actions requiring an internet connection to the VPN (internet browsing, downloads...). You can turn this feature off and then selectively select the domains and IP range you want to send to the VPN.
The Profile field allows you to pick up a name for the selected VPN. Advanced options is where you can configure proxy settings (when required). You can also configure your phone behaves when you are at home (Don't use VPN for home Wi-Fi traffic) or in the office (Don't use VPN on company Wi-Fi).
Once you have configured your VPN profile go back to the VPN settings page and tap on Options. From this menu you can configure the following options: Allow VPN over cellular data and Allow VPN when roaming over cellular data.