Different browsers show your web page in slightly different ways. There are a lot of contributing factors on how your page will look, not just the browser make but its version, how the user has set it up, their screen resolution and so on.
The most widely used browsers are Internet Explorer and Netscape, many now use Opera too. But how do you make your page work well in them all?
I haven't got any easy way to fix this, I build pages, test and fix and carry on that way until I'm happy they are compatible. To start with it can be really annoying, finding out that the really nice effect you have in Internet Explorer looks c**p in Netscape but after a while you will get the hang of what works and what doesn't.
I may well be worth your while to build a page with various bits and pieces - images, tables, the works and then check it out in different browsers, play with the code to see how things look dependent on which browser you use to view it.
I have Internet Explorer 6 installed - Netscape 4.7, 6 and 7, Opera 6 and Mozilla 1 installed to check . I use the Lynx viewer at www.delorie.com to check how the pages look in a text only browser, this site also has a viewer to check for backward compatibility in older versions of Internet Explorer and Netscape.
Often it is a matter of finding the middle ground but, it is perfectly possible to write a page that will look good in most if not all browsers.