Angel investors are mainly the first investors, that are taking the biggest risk and providing first money (investments are smaller than from venture capitalists).
Angels are typically after the same thing VCs are after: equity in the company. However, usually Angel-lead rounds are smaller because the money is coming from the Angel's personal assets (whereas VCs invest larger amounts of other people's money).
When an Angel invests money in exchange for equity, there is no interest involved. They are banking on growth, success, and ultimately an exit that will return them their original investment + X.
There are exceptions, however. An entrepreneur could choose to raise a debt round from Angel investors, in which case there may be interest involved. It really depends on the deal. Nowadays convertible notes are somewhat popular. This is a form of debt that gives the investor an option to convert the debt into equity, typically at a discount, during a subsequent raise.
Angel investor typically an individual who is very rich and seeking to invest some of his money on innovate projects done by others. If you have any innovating projects you can contact Angel investors with your project proposal. So, that if they likes your project they will invest some amount on your company.
Regarding share percentage. It varies according to country, amount requested, your customers number and many criteria(s). The normal estimated share to the Investor is 8% of life time profits or 25% of first 10-15years of profits. Angel can enjoy profits as well they bear losses too.
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On its way to becoming the next Google or IBM, a startup typically receives investment in cash from these sources: