MikroTik

Hi all
i have AP for android can connect to internet without internet in my mobile
its free internet over VPN
(TroidVPN )

but its bit good
working sometimes and sometimes not

so
[*]what if i configure VPN server in mikrotik and this program (TroidVPN ) or any other way connect from mobile to it MT VPN Server
because free VPN servers not satiable and disconnect
but i don't know the way
thank you..
i want get free internet to my mobile every where i connect to my mikrotik server by my android mobile

ok ok
how i can configure vpn server with static IP via WAN

i am working now with PPPoE Client with Static IP from ISP
hotspot and dhcp server

Any Help
my isp static ip is 41.20.20.xxx
i use pppoe client
hotspot + dhcp
how i configure vpn server
my mt is MikroTik RouterOS 6.43.7
model RB951Ui-2HnD