I switched from normal liquid shampoo to my home made shampoo bars a couple months ago. I love my shampoo bars but I know there can be a bit of a learning curve.
I recommend using an apple cider vinegar rinse before you switch to a shampoo bar. That way any build up from your old shampoo goes away. Traditional shampoos can leave a residue on your hair so to truly test the bar I think a rinse helps. Just use a couple tablespoons to a quarter cup of ACV and poor it on your head straight or mixed with water, then rinse it off. I do this about once a month now just because it leaves your hair super soft.
To use a shampoo bar all you have to do is get it wet and lather it up on your hands. Once your hands are all sudsy rub your hands through your hair like a normal liquid shampoo. Then rinse it off really well. Any unrinsed shampoo will leave your hair feeling greasy. It’s that easy. The only thing not to do it rub the bar straight on your head, it won’t feel great and it won’t work well.