When you add a link to your website to another OUTSIDE website, it’s best practice to have that link open in another tab/window. This allows YOUR site to stay open for the user, increasing the likelihood that they will continue looking around on your site after they finish with the link that opened.
Keeping people on your website will not only increase the chance that they will learn more about you and perhaps connect with you in the future – it also has a positive impact on your search engine (Google) rankings.
For links that are WITHIN your website – say, from the Home page to the About page – you should leave the link in its default state, opening in the same browser tab and window. You want to encourage a user to click around from page to page in your site, and opening a new tab or window for every click would be incredibly annoying!
Whether a link opens in a new tab or a new window is determined by the settings that an individual user has made to their browser. Website managers can set links to open in what ever “new” option the user has chosen.
How to set a link in WordPress to open in a new tab or window:
The hardest part is that the next time you open the Insert/edit link popup, the “Open link a new window/tab” will be checked by default. You will want to develop the habit of making sure this box is checked/unchecked as needed. Staying on your own site: unchecked; taking the user to another website: checked.