What have you tried and what specifically isn't working?
Are there connection attempts in the log?
Have you configured IP pools and assigned them to the PPP Profile?
Have you configured secrets and assigned the appropriate service and PPP Profile?
I just got PPTP VPN working on my RB951 (v6.23) and these are the steps I took (using WinBox). Not sure how different the IPSEC L2TP setup would be but maybe this will help.
- Go to IP-->Pools and create a new pool (I called mine VPN). Assign a range of addresses. Since my setup is very basic I just gave it the entire 192.168.89.0/24.
I already had a DHCP pool for 192.168.1.0/24
Next go to PPP and select PPTP Server. Make sure the check box to enable is marked and select the default-encryption profile. Click OK.
Select the Profiles tab and double click the default-encryption profile. For Local Address choose your DHCP pool. For Remote Address choose the VPN pool created earlier.
Next go to secrets tab and create users. Probably best to create a single test user for now. Give them a username, set a password and set service to any or choose the specific service from the drop down. Select the default-encryption profile and click OK.
Now go to the Interface tab and click the + and select PPTP Server Binding from the list. Give it a name or leave the default and click OK.
Next is to create a firewall rule to allow PPTP traffic into your public facing interface. Go to IP-->Firewall and create a new rule. Chain is Input, In Interface should be your public facing (WAN) interface. Protocol is TCP and Dest. Port for PPTP will be 1723,47. Action is to accept. Check the box to enable logging and add a tag if you'd like so you can search (depends on how verbose your logging is). Click OK and place the rule above default deny all rule.
You should now be able to log in via PPTP VPN connection. Try and you should see entries in the log. If you don't then a firewall rule is likely killing the connection. Move the firewall rule created earlier above any deny rules that could be interfering. Hopefully some other, more seasoned folks can chime in with some better help.