First - I'd say give up with the sour dough for now, there's quite a knack to it - not a good idea for beginners.
2nd make sure your yeast granules are active by adding 1 teaspoon of sugar and 2 1/4 teaspoons of yeast (one envelope) to 1/4 cup of warm water, then wait 10mins, If the mixture bubbles up and smells yeasty, then it's ok.
My ingredients for a simple loaf for beginners.
400g strong bread flour (I sometimes mix in other flours, or porage oats (my fav!) but always start with 300g strong white)
2 tablespns of oil or butter
1 tablespn of milk powder
1 & half teaspns salt
6g EASY BAKE yeast
1 & half teaspns sugar
260g lukewarm water
Bung it all in a mixer or a breadmaker and leave to knead.
Tip out into an oiled basin, cover with plastic bag or cling-film and leave 'til doubled. The colder the weather the longer it takes...
Punch it down and tip out.
Either shape into a loaf and put into a tin, or for rolls, cut the dough into 8 or 9 pieces and roll each into a ball. Flatten slightly and place on a baking tray. They do spread a little during the 2nd rising so don't put them too close together.
Leave to rise again with oiled plastic or clingfilm draped gently over them, once risen bake at 180C fan - gas 6 for apx 20mins for rolls, apx 30-35mins for the loaf.
Tip out of tin to check that the loaf is cooked at the bottom, return to oven for 5mins if the bottom is still soft.