Assuming that you've already installed the MerchMixer App on your Shopify store (and looking at the MerchMixer dashboard), the first step is to click on the "Find Products" tab.
You have several ways of searching for products on MerchMixer. One is to simply type in the keywords on the search bar. For example, you can type in "iPad" and it'll automatically show you a list of products that match your query.
You can also search for products by category. Click on "All Categories" and a drop-down menu will appear showing the different product categories available. Choose one that is most relevant to your niche (cellphones, for example) and it'll show you a list of products that match your search.
You can filter products by cost. Simply click on the "Cost Filter" and assign a price range. This is useful when you're looking to sell products at a certain price range.
Click on "Sort by" to sort products according to price, item cost, newest and order count.