Wiring for Dummies -101 ... Need advice

[6600DURAMAX]

I do not know what else to call this post other than that.....

I need some advice / guidance on how to understand wiring

Trying to understand relays - how they paly a part - is the fuse panel sufficient enough or is their another in-line fuse needed in situations ??

What I have
1- New Painless complete wire harness
2- PSI LS3/6L80e Wire Harness
3-Duel Electric Fan setup
4-Aermotive Stealth 340 In tank Fuel Pump

Lets just start with Fuel pump - I thought that would be easy enough but I'm confused - both the Painless and PSI harness have wires for fuel pump. Do I run the hot wire from the fuel pump to the Painless harness ? Is that my "fused" connection -- then I run the PSI Fuel pump wire to the same terminal on the Painless harness?

Fan - same situation - have a spot on the Painless harness for fans but then the PSI Harness Diagram also has two separate wires for fan control. Then when I look up the Spal wiring diagram it shows fuses and relays - how do i separate what is needed and what is not ?