There are a variety of different Arduino boards, each with a slightly different purpose. The most common one is the Arduino Uno, which is a good allrounder and suited for many tasks. If you need more connections and processing power, the Arduino Mega is your friend. If you need to go tiny, look for an Arduino Mini. In addition to that, there are some more specialised Arduino boards available.
An Introduction to Arduino Uno PinoutBlog PostAnat ZaitApril 22, 2018