The first thing you do is determine your team cadence (collaborative decision) - will you do 1 week iterations or 3 week iterations? if you don't know, start with one week. The idea is to get into a rhythm that you will repeat, and experience has shown that starting with short iterations is best. Once you have your cadence defined, you split the feature into a set of stories that can be implemented within one iteration. Stories should show some value to customers - even minimum value as "login in". Stories are then estimated in detail and scheduled into iterations, in priority order defined by the product owner. Priority order should reflect customer value, but you may also have to consider story dependencies - maybe one story must be built first (such as "login in") for other stories to work. And you keep doing iterations until the "feature" has enough value to release to customers. At the end of each iteration, you check with customers whether you are on the right track, and you adapt the stories for your next iteration accordingly.