Hi Anis, so think of your base shape following more like the blue ink here:



Then later to make that ridge line you will cut something like this area out and put in some new surfaces in there, probably with Blend:




For using surfacing tools for the initial shape, you will probably want to use something like Revolve or Rail Revolve, as those give the most natural kind of revolved or domed type surface shapes with nice shaping at the "pole" areas. It's otherwise quite difficult with other surfacing commands to make a pleasant smooth dome shape at the point where all the curves collapse together.


- Michael