I'm not sure I'm following you, Hawkeye. Constructors run out of resources if the space port they're pulling resources from has a low supply of whatever resources needed for the construction job. Reducing constructors range shouldn't offer any help whatsoever in terms of reducing the risk of a resource shortage. And I don't really encourage using the resource planner too much either, since it doesn't offer much help in building mines close to where they're needed. It also tends to have really odd priorities, telling me that there's such a thing as enough hydrogen or chromium. :-)
im !!!!!!ALWAYSˇˇˇˇˇ out of resources in my colonies and the worst problem is that i dont build !!!!!ANYTHINGˇˇˇˇˇ at all every colony that i have is like resources shortages are hampering the colony
There are a few things that might cause trouble here. The default automation of colonies might be causing them to build stuff, be it bases, constructors, or colony ships, and in that case you might run into problems. Alternatively, your number of space ports might be either too low or too high. You'll want to have enough that a stockpile is reltively nearby but not so many that your freighters have to take all kinds of resources everywhere all the time. Building a space port on every colony is bound to cause havoc eventually.
supposedly the moving of resources or the transport of resources or whatewer you want to call it is by the private sector of your empire so you must low your taxes so you can have a better and constant system of resources very well distributed in your empire.
Taxation doesn't directly affect your resource distribution. I think it's much more important to make sure your civilian freighters are somewhat up-to-date with a good hyperdrive, enough thrusters to reach a cruise speed of 20-30, enough cargo capacity to actually make a difference, and enough fuel capacity to get around. Typically, even my small freighters have a cargo capacity of at least 3000 and a range of at least four sectors and my goal is twice as much, once the available tech makes it feasible.
The freighters are only one part of the resource distribution, though. The number of stockpiling locations is another. If you've got space ports everywhere then you'll have loads of places trying to stockpile resources, which I think is a stress factor on your civilian freighters. If you keep a good distance between your ports, there'll be more freighters per port and thus a more stable resource supply.
I have no idea how the system of trade works in this game
I don't think anyone really does. As far as I know, there are independent traders and there are alien civilian freighters. Both can fly to your space stations and planets and trade resourcecs. That's trade. There's more of it if you've got nearby alien factions that you're somewhat friendly with and even more if you've got resources that the other faction needs. I think a free trade agreements adds a bonus to this but I can't say for sure.
when you do a mutual defense pact with a species you are not any longer trading resources
I'm pretty sure you'll be trading with other factions regardless of diplomacy. Mutual defense pacts are really just a way of declaring to the galaxy that you and the pact brother are best buddies 4 lyfe, for whatever a close friendship with an AI is worth.