If you ask me how long does it take to start speaking to be understood? My answer would be – 1 year. In a year you will be able to deal with issues at airports, hotels, do the shopping and communicate with people from all over the world discussing common topics.
If you have more ambitious goals and you are keen on getting really good linguistic skills, you will have to study for 2 years or more. Sure, studying English (or any other language) is quite hard. But having a good motivation you will be able to deal with any issue. Moreover, you might find studying really fascinating. You will open a new world for yourself!