"I can view the website made by me in my own computer but i can’t view it from another computer."
That's why it is important to provide enough details. I thought you were getting errors when configuring your apache server because of this part of your question: "...is in use by another program"
Please, keep in mind that we don't know your set up nor do we know what you are trying to do or how you are trying to do it, so we need you to provide all the necessary details to help you troubleshoot the issue.
Gabe9527 suggested turning the firewall off. That would be the first thing to try. If that doesn't work, then answering the following question would be a good idea (please be specific):
"But according to my windows Firewall it is used by another process"
How (and when) exactly is the firewall telling you that the port is used by "another" process ?
"I can view the website made by me in my own computer..."
How are you viewing it ?
"...but i can’t view it from another computer."
Are you talking about another computer on the same network ?
How are you trying to view it ? (what is the URL you are trying ?)
P.s. I have removed Harisheldon1960's answer from the Wiki, since it was incorrect and misleading.
Port 80 is used by your browser for web surfing, it is defaulted to that. Unless you configured it to something else, or someone is playing games with you, it is always open and ready for the Internet.