I am a bit confused about the meaning of these two terms:flavor and version,i know its a very basic question but i am a beginner so please explain it with some example that what they two mean and how they differ ?
Flavors are the various editions of Ubuntu depending on your need, your preferences and your hardware. E.g. Lubuntu is mainly for old computers with little resources, Ubuntu Studio is for multimedia creation, Ubuntu Mate has a classic desktop, etc.
You can read about the flavors on https://www.ubuntu.com/download/flavours
The versions are the new updates of each flavor. New versions are released twice every year, approximately in April and October. So, Ubuntu 18.04 was released in April 2018, Ubuntu 18.10 in October 2018, and 19.04 will be released in April 2019.
Each April version from even years (14.04, 16.04, 18.04 etc) are so-called LTS (Long Term Support) versions, which are updated for five years. All other versions (i.e. 16.10, 17.04, 17.10, 18.10, etc) are regular versions which are updated for nine months only. So, if you want to avoid having to update the entire version too often, it's better to stick with a LTS.