configuring mikrotik router attached to three moderm-router

hi to all of my dear friends…
i need your help…
i’m a beginner to mikrotik and i gotta a problem with configuration of my mikrotik router that drived me nut. 
the problem is that i have three modems that each of them providing internet from a specific ISPs. (it means that i have three ISP)
therefore i have to have all these three modems in my network in order to if any of these modems failover, the other must one supply internet (by routing).


1-how must be modem configuration? in terrms of ppeoe or bridge connection? and what IP i must give to the modem?

2-do i need three WAN interface in winbox for those three Ethernet ports of mikrotik router that occupied by three modems? or it can be performed by one WAN interface also?

for configuring the LAN interface, i think that i must build just one interface (typically ether4-lan) by ranging IP for example 192.169.1.1/24

could you please send to me full manual of configuration (from start to end) for both of mikrotik and modem routers??
by the way, my DNS servers are: 217.218.155.155 ---- 217.218.155.127 — 46.224.1.221 —46.224.1.221 — 8.8.8.8 ---- 10.201.32.162 —10.201.32.163

thanks for any help.
my best regards…