If you spend much time researching breadmaking, you’ll find many references to the term “hydration level” following by some percentage. This is simply the ratio of water to flour by weight in the bread. For instance, a 100% hydration dough would have equal parts flour and water. A 70% hydration dough might have 1000g of flour and 700g of water.
Higher hydration doughs are more difficult to work with but tend to produce large holes and a lighter crumb. I recommend starting with something lower hydration and working your way up as you become more comfortable. I don’t always have a scale, and I find that a reasonable assumption for the weight of water is 240g ≈ 1 cup. Flour weighs about half that. At first you may rely heavily on measurements (which is fine!), but as you grow comfortable with baking, you’ll be able to tell what the dough needs based on the way it feels.