Measuring amperes, what the reading mean?
All of the settings with "m" in them represent milliamps.  The "setting" is what we call the range, or the "full scale value".  It indicates the highest value that can be read without being "out of range".  The reason the readings look different is that the precision changes.  Specifically, .600ma is the same as 0.6ma.  It's also the same as the 0.5 reading (shown as "00.5") but you'll notice it is "off by one count".  This is what happens when you measure something that is a tiny fraction of the full-scale value.  The accuracy of the measurement suffers.  And that's why you should choose a range that is comparable to what you're measuring.

The remaining measurement was done on the "20" scale, which is 20 Amps.  You got a reading of 0.05 A there, which would be 50mA, but that's just too far "down in the noise" to be useful.