Yahoo stores are somewhat limited in function compared to other solutions but they do bring in traffic from Yahoo's shopping network which is where their real value lies.
Most online services revolve around PHP tied into MySQL databases to run the actual functions of the site with HTML and CSS to control the appearance and interaction with the web browser.
I've built many successful sites and I know very little HTML, CSS or PHP. I can hack out a few lines here or there but mostly I've realized that for simple things there is almost always a commercially available solution out there, and for complex things I'm in over my head and need to hire a pro.
Having the skills are good though because if you (for example) hire a programmer to create a solution you will be able to make small changes without having to pay someone else to do it.
Just don't get "feature creep" where you feel that there is always one more thing you need to add or learn before you start running with your ideas.