I started my starter with flour and water, no added yeast. The flour carries the critters you wish to cultivate.
A simple way to start is a 50/50 mixture or flour and water by weight. Let it sit loosely covered for 12 hours. Feed it and let it sit another 24 hours.
You might see some activity at this point, but you can feed it again. I would wait another 24 hours for activity then feed. You might get a bit of a unpleasant smell up to now, just keep going. After the next feeding start 12 hour feedings.
When you feed mix equal parts starter, flour and water by weight. You will need to discard some starter or you will overwhelm yourself. I usually do 50g unless I know I will be making bread then I increase to 75g. (50g = 150g mixed, 75g=225g mixed).
Before you use the starter for baking it needs to be able to double itself (at a minimum) in 12 hours (the feed cycle). If it can't raise itself it won't raise dough. If your starter is sluggish or you want to help jump start the feeding you can take a bit of rye flour and substitute it in for some of the flour. For instance 12g rye + 38g white flour to add to 50g water.
When you mix you don't need to get it smooth, lumpy is fine. Make sure the container is clean, you are cultivating bacterias and yeasts, you don't want the wrong ones in there.
You can refrigerate the starter but I wouldn't for a while, you want to give it time to get happy and find its way. The 4-6 weeks it is best to just feed on a 12 hour cycle and keep it in a warm place (around 80F).