Web Presence means few things,

• the existence of business  on the Internet in the form of website
• the image a e-business projects to its customers, suppliers, employees, and stockholders.
• Attraction and traffic driven of the website

Check out the following sites regarding Web presence and Usability

• 3 Keys to a Successful Web Presence
• Establish a Web Presence
• Why an Organizations needs an effective Web Presence?
• Ten ways to improve the usability of your ecommerce site

Electronic wallets (aka Digital Wallet) is  a storage medium to securely store customer’s private information like name, address, phone number, credit card number, etc and display it on a merchants’ form without manually typing on the form.

Here are some links to read about it

• Digital wallet
• E-commerce – Overview – Digital Wallet
• How to use Yahoo Wallet

Electronic Cash is fairly new payment method  for e-commerce.  Read on wikipedia about Electronic money, which is also known as electronic cash

Early form of e-cash is introduced by David Chaum. David Chaum invented Digital cash. Read about it here.  (For additional reading, click on Electronic Cash)

PayPal is an example of Electronic cash System. Read about PayPal and  visit How Does it Work?

Merchants and developer should first test their PayPal transaction in  PayPal sandbox environment.   (Sandbox User guide)

Additional documentation from PayPal are available here

Payment methods, specifically payment processing is extremely important  in E-commerce.

Start by reading about The history of credit cards

Here are some contents related to this topic

• E-commerce Payment Methods
• Which e-commerce payment methods do you offer?
• Web Hosts And Payment Methods
• E-commerce Payment Methods from Optimum7
• Different Payment Methods In E Commerce Website

Information about payment processing

• How Credit Cards Work
• Card Processing Basics
• How does online credit card processing work
• Online Payment Processing And Payment Gateways
• Credit Card Processing: How It All Works
• E-Commerce Payment Processing Beyond PayPal

Information about Payment service provider

• Authorize.Net: What We Do
• Authorize.Net: “How It Works” Diagram
• Authorize.Net: Advantages of Accepting Payments with a Payment Gateway and Merchant Account
• Nochex: Internet Merchant Services

The Payment Service Providers have to comply must meet certain standard to protect customer credit card. Visit PCI DSS for more information

To best decide the right Payment service provider for your business, check  Credit Card Processing Review and  Payment Processing Tips