@levankup777 Using DAX unlike Excel you can't access previous row so you need to use order of year to access previous row value. So first create a new column with code as below to access previous row value. I created sample csv like your scenario.
Once you get previous row value, use below code to get percentage difference and apply percentage format to column.
Column 2 = (sam[Value] - sam[Column]) / sam[Column]
you say you need a chart with monthly information (bars), but you haven't provided any Information at describes how your data is structured. You should have a data table and a calendar table.
Read here about data structures
and here about calendar tables
In your scenario, you can create a new table to list records for each month in year 2015 like below:
Then use the method provided by @ankitpatira to calculate difference between each month within year 2015.
If you have any question, please feel free to ask.