1) How do clear cookies from the cache of a macbook?
You don't. You clear the cookies from your
browser, not your machine. Cookies are browser-specific, and each browser you use has its own cookie database and way of cleaning it.
Pretty much all browsers, though, have some option in their preferences to view and delete cookies.
That said I doubt it's the cause of your problem. For some reason people like to point fingers at cookies when, in reality, they are rarely the problem.
2) Is there any other reason why my internet may be so slow and/or timing out so often?
There are many, many reasons why your connection might be slow. The first test is to try a different browser (or even a different user account with the same browser). Since each browser (and each user) has their own cookies then cookies might be the issue if the problem goes away.
Beyond that there are DNS server issues, proxy server issues, network configuration issues, bandwidth issues, wireless interference issues, and more.
It would help if you could narrow down/identify
what is slow. For example, are you talking specific sites? Is it slow the first time you load a page but a refresh/reload is faster?
Are all internet connections slow? or just web? (what about mail? file transfers?, etc.)
Do you have other machines on the same network? are they experiencing the same slowness?
If you're using Safari, do you have the Status Bar shown? (view -> Status Bar). What does it say while you're waiting for a page to load.
Also in Safari, what does Window -> Activity have to say while a page is loading?
