Baking – Simple stone ground flour bread

Bread is basically just flour, water, and yeast, so it's pretty hard to make it inedible unless you burn it to a crisp in the oven.

The difference between all-purpose flour and bread flour is gluten strength; if you substitute all-purpose flour then your bread won't rise as high or be as strong; this is a desirable quality in, say, cake, but not bread.

However, AP flour isn't that far off from bread flour in terms of gluten; while cake flour may be as low as 6% and bread flour can be as high as 14%, AP flour tends to weigh in at around 10% or more, which is why it's called "all-purpose". As Michael says, yeast bread is actually not as sensitive to the exact quantities as (for example) most pastries, but it's still better to use a recipe that was actually built around AP flour instead of just trying to substitute it for bread flour.

If you are determined to make the substitution, then I would suggest you try to find some wheat gluten and add a small amount of that to the AP flour. Mathematically, if you assume that you're lacking some 3% protein, then you'd want to add about 1 tbsp of gluten for every 2 cups of flour. It's really not much, though, and if you don't have or can't find wheat gluten then your bread would probably survive anyway with AP flour, it just might be a little denser than you expect.

"Strong flour" and "Bread flour" generally mean the same thing -- lots of gluten, so the dough can stretch and incorporate lots of bubbles.

Not all bread demands high-gluten flour, but the traditional airy loaf of Western Europe and most of the USA does.

If what you're making is bread of that kind, "strong bread flour" is what you want.

If you're making a cake or a sauce, things will probably be fine -- try it. It might not be perfect but it won't be a disaster. It's worth having some less strong flour (often labelled as "plain flour") in your store cupboard.