- Go to the site you want to use as your homepage. (Yahoo.com, etc).
- Go to Safari Preferences.
- In the General view, make sure the option "New windows open with" and "New tabs open with " are set to "Home Page", and then click on Set to Current Page.
If you don't have a favorite page that you like to go to, consider setting both "New windows open with" and "New tabs open with" to "Empty Page." Since you won't have to wait for a page to load before you continue, you can get about your surfing faster.
Another suggestion is a mix of the two above suggestions. Set "New windows open with" to "Home Page" and then set "New tabs open with "Empty Page". The result of this setting is that when you open Safari (or open any new window) you will get your home page that you want to see. But when you open a new tab on that page, you don't see the home page and can get right to work.
If you would like some inspiration for a homepage, Apple provides a large number of interesting bookmarks you can check out. Click the book icon on the far left of the Bookmarks Bar. There are folders there for Mac, Kids, Sports, Entertainment, Travel, Shopping, and Tools & Reference.
Another option for your home page is Top Sites. Top Sites shows a thumbnail grid of the websites you visit the most often. It can be pretty slow to load, but I know that many people like it.