How do you get to these sites? A couple of ways. 1) You may have searched for something like The Red Cross and the first site that popped up was wrong. 2) You may have clicked on an ad for the site but it was a fake.
The best way to be sure you are at the correct place is to type their actual web address. For example The Red Cross is www.redcross.org If you do go by way of a search engine just make sure the address, on the top of your browser, begins with the proper name. Any site like give.redcross.com will be fake.
Also no charity will ever ask you for a password, social security number, birth date, etc. If they are asking those questions they aren't legitimate.
Also remember the same thing can apply for telemarketers posing as charitable organizations. If you aren't sure you can check them out at www.ftc.gov/charityfraud or bbb.org
Another great recourse to find good charities and advice about safe donating is charitynavigator.com