I've lived in a house I've owned for almost 20 years. Now wait, you are thinking, you already bought a house, what are you asking this for? Well, let me explain.

The house we live in, we moved in on a lease-to-own deal. The owner applied a percentage of the rent to the down payment, which two years later, she handled the mortgage transfer, and boom, we were homeowners.

So where I am clueless is... I want to.buy a new, bigger house... but do I have to wait for my old house to sell? With the market today, how do I "make an offer" on a house I want without knowing exactly how much equity I have from the sale of my house? Will the realtors that are selling my house and the realtors selling the house I'm buying get together on the sales particulars? And what about the new mortgage vs. the old one? Can i carry two mortgages at the same time until the money from the sale of my house both pays off the old mortgage and transfers the "down payment" to the new one?

I'm sorry if you are slapping your forehead right now wondering how.someone can be so clueless, and believe me, I feel the same way that I just don't "know this", like it should be common fucking knowledge for a functional adult.

Someone please give me a ELI5 or some rudimentary step-by-step so I dont look like an idiot.