"Indicator tester" is a block that can be used to visualize values on the chart, similar to indicator. This block is to be used when you don't have an idea what the custom indicator buffers are giving you. It's an alternative to the native Comment for example, but it also prints the history of values as a line. This line is created from multiple small trendlines, so it's not a good idea to use this block in normal situation. Use it only to see what is going on in custom indicators or other values.
After you add a new indicator, reopen the properties window of "Indicator tester" 
EX4 files are all that MetaTrader 4 needs to run the expert advisor. This is it's compiled version, it's "executable"... the expert advisor itself. What is needed is to put it in the directory where other Experts are, open MetaTrader 4 and double-click on it in "Navigator" or backtest it.