Online investing?
As a former investment professional, I would recommend staying away from any online trading/investing, especially those who "promise" immediate/high profit. There is a lot companies out there who prey on unexperienced investors. Our friends recently lost their entire life savings, $30,000 to an unscrupulous "firm".
When you invest with a legitimate broker/dealer, they will have procedures in place to protect you as a client (required by law). Each transaction will have to be reviewed by a principal (my old job). They have a compliance department. They can be randomly audited by SEC and NASD. They have insurance. They must disclose all their fees in writing.
Little Internet firms often flying under radar? I am not so sure.
Seriously, don't do it unless you know what you are doing and don't listen to friends or relatives who supposedly made huge bucks. The risk is too high especially if you like a lot of MT's are not exactly rich.
Market is unpredictable; we don't know what is going to happen tomorrow or even a few hours from now. Millions of factors determine the cost of each security. therefore, anyone promising guaranteed returns is lying through their teeth.
If you would like to start investing, I would recommend meeting with an investment rep. As an inexperienced investor you should stick with well known firms (Charles Schwab, Robert W Baird). IMPORTANT: The rep should meet with you FOR FREE and review your investment goals. Stay away from reps who will charge you upfront and when you are meeting with someone, resist sales pressure or guilt trips (That they spent a lot of time meeting with you and now you HAVE to buy from them). There will be fees to invest with a rep (either loads on mutual funds - upfront fees OR a flat fee).
You can also educate yourself by visiting web sites of companies like Vanguard or Fidelity. Both are very reputable companies and have very good information on their web sites as well as hundreds of mutual funds to choose from. And low fees!
Another good resource is morningstar.com - this web site rates mutual funds and stocks/bonds etc.
Good luck and be careful out there!