Hi PastaPrincess! Welcome to the wonderful world of baking!
There is indeed a difference between cooking and baking. Baking requires precision in measuring to obtain the right results(although quite a few holdouts such as my elder sister still insists she never measures, AND she does bake quite well). There's a lot of science going on in reactions between different components in your average cake, and you have to have the right ratios between those ingredients.
One fix I found that helped me out was to switch from measuring to weighing flower. Since flour compacts, it can vary greatly depending on how you get it into the measuring cup. When you weigh however, 6oz of four will always be 6oz of flour, no matter how much you squish it together or spread it out. All Purpose flour weighs approximately 4oz(for a cup).
If that's a bit too much to deal with, I'd just be sure to always use a measuring cup with a smoothable top, and to lightly scoup flour into the cup, tap the cup a few times, and then level the top with a straightedge.
Another thing to consider is the source of your recipes. If you never made a recipe before and obtained it from an untrusted source (such as the internet) several things could be wrong with it. Some are easy to fix...for example... those fridge biscuits. Now that you made them once, have any ideas on how to make them taste better? a little less butter? or if you were using a butter substitute maybe just stick to good ol' butter, which the recipe was made with originally? As for being brittle, let them set out of the fridge a while and see if they still are.
Baking is harder than cooking, I'll agree to that whole heartedly. I have had my share of great successes and horrific failures in this arena.
Another point also, is that humidity affects bakers quite a bit. flour weighs heavier on more humid days, and may affect your overall recipe. There is no cure or quick fix for this, aside from learning to adapt through trial and error.
the best advice I can give is to keep it up, and don't quit from a few failures!
You can only get better.