E-commerce allows for the buying and selling of products and services over the internet. It provides advantages like faster transactions, lower costs, and the ability to start an online business without a physical location. However, disadvantages include a lack of quality guarantees, the risk of mechanical failures interrupting transactions, and the threat of hackers targeting payment systems. The top five e-commerce sites in Nepal are listed as www.muncha.com, www.kaymu.com.np, www.rojeko.com, www.bhatbhatenionline.com, and www.meroshopping.com.