Many guides on creating sourdough can be found online. These are good:

• I ruined 8 sourdough loaves [so you don’t have to]
• Step by Step Beginner Sourdough Tutorial - Perfect Recipe for the total Sourdough Newbie!

For example:

• 60g active starter
• 340g water
• 500g whole wheat flour
• 10g salt

Mix into a dough with a wooden spoon.

Repeat around 4 times as needed to build elasticity:

• wait a half hour, then
• lightly stretch and fold the dough in on itself

Allow the dough to rise at room temperature until it has doubled in size (4-12 hours). Bake covered 450f for 30 minutes.