The ISP they know everything I send and receive over the Internet including my emails and messages right ? So I am wondering if there is a way to prevent them to do it ?
http://www.cypherpunks.ca/otr/ for instant messaging, http://www.gnupg.org/ for emails. Make sure to exchange keys through a secure channel, if they are compromised all your efforts are wasted. Using SSL where available should be a no-brainer.
End-to-end encryption is the best solution as noone can spy on you then, but if it's all just about your ISP, then SSL encryption should be enough.
That means using only
Regarding the e-mails, it's probably best to use PGP which is end-to-end encryption. The recipient, however, has to use it, too.
As to browsing the web, you might be interested in VPN or Tor (slower, safer). This, however, still doesn't stop exit nodes and the server from seeing what you are doing - so, in the end, end-to-end encryption is still a must if the privacy really matters.
If you use Skype for IM, note that Skype encrypts its communications.
Regarding email, If you use webmail, and your connection to your email provider's website is HTTPS, and you've verified that the HTTPS certificate is actually from your email provider, then your ISP can't see what you are doing on that site.
If you are using a standalone email client such as Thunderbird or Outlook, you need to make sure SSL and/or TLS is selected/enabled when you set up the account. You may need to consult the email provider's online help to determine what settings to use (i.e. ports, servernames, etc.)
Note that most of this only ensures your ISP cannot see your communications. You have no way of controlling what the remote end does with the message, or if it encrypts upon transporting to the recipient. So it is not an end-to-end encryption solution that will prevent eavesdropping completely.
Now, if end-to-end encryption is what you want, use OTR as @Squeezy suggests. This lets you add encryption over various existing instant messaging services - transparent to you if you are using the plugin. It's a plugin for the open-source multi-protocol IM client Pidgin.
End-to-end encryption for email is possible, using PGP or GPG, and there are plugins for Thunderbird and (possibly non-working, non-reliable) plugins for Outlook. Both ends have to have these plugins installed and the proper keys installed beforehand (which you don't want to transmit via email as that defeats the entire purpose.) Claws Mail may serve your needs if you can get your recipients to use it.
In a pinch though, if you and the recipient know a shared password, using an encrypted (i.e. "password-protected") zip file to contain your message should be pretty good. Use AES-256 or higher if you can. 7-zip is a free program that allows you to easily do this with a right click.