Each time a visitor access your blog, the wordpress script would have to go through a process of gathering up every single thing you see on the blog page. The long process would include the PHP code making number of calls to the database to fetch information and tables. This process could happen 10 – 400 times when each page is loaded. This slowness can be reduced by using a feature called “caching”.
Once caching on the server is enabled, only the first visitor accessing your blog page would have to go through the lengthy process and the caching system would store the results in a cache and serve the same for the subsequent users. The method speeds up your blog to about 50 – 200 percentage than normal processing.
I have tried and tested almost all the new and old caching plugins available for use on the wordpress system and have listed the plugins based on their effectiveness on caching. This could help you choose the best caching plugin for your blog and speed up your visitor’s browsing experience.
you could find the Best wordpress caching plugins here