If you set up www.yourdomain.com in Weebly and have MyDiscountDomains.com as your registrar it may not be obvious how to make yourdomain.com work when you put it in a browser.
So you may already have bought your domain yourdomain.com at MyDiscountDomains.com.
So when you set up your Weebly site initially it will be given a Weebly subdomain as its link and you can read all about Weebly and domains. In particular, you can get advice on how to manage DNS records. However, it's a little bit different in MyDiscountDomains as it uses a blank (nothing typed) instead of @ for the root.
So login to MyDiscountDomains.com. You will see a list of your domains and next to each domain under Edit click DNS.
Click on DNS then look at A records.
Weebly will give you the IP address, most likely 199.34.228.xx where xx is some number - type in that number not xx.
Note under Subdomain, you leave it blank for yourdomain.com, www means go to Weebly and * means anything else - you might change this later for example, you might want maps.yourdomain.com to go to a map on another server with a different IP address.