When the flour, yeast and liquid have been mixed into a dough, it must be kneaded until smooth. The idea is to stretch the gluten in the flour so the gas that the yeast produces can be trapped, lifting the dough.
Flour varies from brand to brand and some absorb more liquid than others. Start off with a soft, slack mixture, reserving a little of the recipe’s flour. You can add more flour as you go to no ill effect but adding more water is difficult.
The method for kneading is this: flatten the dough by pushing it forward with the palm and heel of your hand, then fold it back toward you with your fingers. This should be done full force, leaning and pushing against the dough with all your strength.