One of the easiest forms of investing is via purchasing an ETF (Exchange Traded Fund). This investment form has first been introduced in 1993 and by today it became extremely popular. In 2015 there were over 4,000 different types of ETFs, therefore the choice is endless.
An ETF can suit almost all kind of investment needs from simple index ETFs (e.g. VTI, which represents the total US stock market) through sector ETFs (e.g. VFH, which represents the US financial sector) to some really wide spread investment vehicles (e.g. GIVE, which holds both US and global stocks, just as bonds, all focusing on environmental friendly and sustainable themes).