Many website builders shy away from outbound links but used correctly they can help your SEO immensely. In fact search engines will give you brownie points if you link to the right websites because ultimately you are helping internet users find what they are looking for.
Good quality content usually refers to its source so links within your content to other sites which back up what you are saying and good quality content is what search engines are looking for.
Not all outbound links are good links. Here are a few examples:
There is a catch22 here. You don't want people leaving your website too soon and so you would prefer that if they did click a link to a different site that site would open in a new window or tab. That way if they close the other site yours is still open and will remind them of your existance.
On the other hand search engines frown on this because they feel you are doing something the user has not asked. If they wanted to open the content in a new tab or window they could so with a right hand click of the mouse.
Personally I've found this 'frowning' has very little impact and I mark all of my outbound links to open in new windows. Where possible I do put a warning next to the link in a way search engines can read - simply something like (Opens in a new window). If the link is in the middle of a piece of text I might use an icon.
Note I say new window, not new tab. When users close the window that has opened they will see your site again. However when they have a window with multiple tabs open they may just close the whole window and you, along with everyone else .... are gone!
There has been some hysteria following the introduction of Google penguin that all outbound links should be marked "NO FOLLOW" just in case. I don't and I've never had a problem. I link out to sites and pages that I believe are genuinely useful and helpful to users. You should to.
I'm Tim Hill, a Search Engine Optimization and Online Marketing specialist. I created this site to help others understand that SEO is not a mysterious black art!.
If your a newbie try the Getting Started in SEO page, otherwise feel free to dig around and learn more.