How can I learn advanced skills in Excel?

NICE QUESTION THERE ARE MANY WAYS TO  LEARN ADVANCED SKILLS IN EXCEL (READING BOOK , WATCH YO TUBE ,FOLLOW   PAGES )

BUT THE IMPORTANT THING THAT YOU MUST PRACTICE WHAT YOU LEARNTO BE CONNECTED  & HAVE  CREATIVE SKILL 

you can try www.officena.net

There are many sources to acquire knowledge and specially, Internet has completed revolutionised things and you are only on a click far from knowledge. Although the best means are books but today there are many blogs, vlogs, websites, you find infinite number of videos on youtube, daily motion. Recently I came across some professional tutors who offer good classes hosted over Skype and please note they are great. 

www.youtube.com here you get almost all what you need in excel. Subscribe to some channel who teaches excel so you are in the loop.

Functions are easy to create in Excel and, by design, they simplify and automate tasks that would otherwise be much more labor intensive. That said, there are a number of functions that, in practice, require some skill in order to solve complex problems. Part of the challenge for you is knowing when and how you can apply these and how to design them for your specific purpose

watch Youtube videos and then Teach everything new u learn to others

There are many ways to do it. For a fast approach, watch youtube videos. Dont forget to practice becuase without practice everything is vain.

Most of the excel functions have help in the EXCEL Software itself. Practice one by one and try to make use of it in daily operations. For Example VLookUp, Pivot Tables, Basics like Sum, Average... If you have doubt and can't understand refer to youtube as well..

Formulas make Excel smart. With out them, Excel is just a data keeping tool. But by using formulas, you can crunch data, analyze it and get answers to most complex questions. While anyone can use a simple SUM or IF formula, an advanced user of it would be able to seamlessly write & combine formulas like SUMIFS, SUMPRODUCT, INDEX, MATCH, LOOKUP formulas. Apart from knowing the formulas, advanced Excel users know how to debug them, audit them and how to use which formula for which occasion (and they also know few alternatives for any given formula problem)

By search in the internet ...

Practice, practice and lots of practice. Keep chalanging yourself.