Thank you so much to those who replied. I really appreciate the time and effort you guys give to help rookies like me 
Skip to main content
That’s true. You have to imagine the voltage as a tank filled of water and the loads as tubes of different size coming out of the tank. They won’t take away
more water that they can handle.
I agree too, my initial reply assumed that you wanted to ensure that you can’t go over a certain current threshold. This would be good to protect devices which might for example short circuit and want to draw more than the amperage it can take causing the device to burn out.
the answer to your question is not a device or technic that limits or suplies the right amount of current but understanding how the amount of current gets there.
The amount of current each device draws is a function of their resistance and the voltage you put on it.
for example, if you measure 1,2ohm resistance and put 12Volt over it that would mean that 10Amp would flow through.
if you would put 24volt on that same device 20Amp would flow trough and if the device isn’t rated for that amount it would probably get to hot, smoke or go boom.
now if for example you would measure 6ohm resistance and put 12V over it that would mean 2Amp would flow through
So you see you can understand how much each (static) device requires just by measuring the resistance of the circuit.
There are also switching elements like transistors that would give you a false reading because it can open and close a circuit changing your measurment.
but for most dc elements like for example a heating element you can measure it this way to make sure how much current will flow trough.
to beter understand what voltage, amp rating you need or how much amp an device will use there are 3 very simple sums.
get familiar with ohms law
https://learn.sparkfun.com/tutorials/voltage-current-resistance-and-ohms-law 3
basically if you know 2 values these sums will give you the answer to the third:
V=I*R
I=V/R
R=V/I
important note: get thick enough wires, you don’t want them to get hot or melt.
make sure they are always rated higher than the amount of current that is actually going to flow trough them.
also it is always wise to have a power supply that is rated for more amp than al devices combined require.
if you try to pull 15Amp from a 15Amp rated power supply chances are you might blow a fuse, the voltage might drop or a short-circuit protector might kick in. so if you need 15Amp its better to have a 20Amp power supply. 
exactly.
because of the amount of resistance to current flow each load draw the amount of current it needs.
changing the voltage higher and more current will flow even with the same amount of resistance.
so you can control the amount of current by changing the voltage, or if you change a circuits resistance.
but don’t try to change the amount of current with wires because a wire has basically zero resistance and will not limit your current flow *except for maybe melting and burning till it breaks…
