No problem O.M. we all start some place and I remember many, many moons ago back around 1970 asking the same question. So time for me to pay my dues.
D.W. the Top scale on your meter is all for receiving. In other words
S" units 0 to S9 - S9 being top dead center at 12 O'clock high. Anything above "S"9 is in the RED scale and you say it as 10DB over S9, 20DB over S9 30 DB over S9 or 40DB over S9. OK on that...
Now for your current scale you read the bottom scale it goes 0 then the next larger marking in .1 / .2 and .3 and .4 and .5 Each of these large
indications show 100 Milli Amps. So at .1 you are actually reading 100 milliamps of Plate current on the final amplifier. At .2 you are reading 200 Milli amps and so on. Typically the FT-101 when used in SSB mode will modulate up to some place around .250 or .300 (300 Milli Amps) when you are talking. Peaking the meter into the green portion of the lower scale.
Each little marking in between .1 and .2 / .3 and so on you see FOUR little markings those are indication 20 milliamps each. The FT-101 when keyed down in SSB mode, with NO modulation should show an Idle current of approximately 50 to 60 milliamps. Again that is key down in SSB mode, either LSB or USB. The meter should rise to a minimal of TWO notches, maybe three and you're OK at 20 Milli amps per marking. IF the reading is above 60 milliamps then it is advisable to turn it down. The way this is done, you key the rig look at the meter and turn down the idle current by using the control on the power supply board.
When tuning your rig key down, keep it brief 10 to 20 second then unkey and give the tubes a break. Then key again in Tune position 10 to 20 second and tune some more, unkey and key the tubes a break. You should never keep the rig keyed down very long and always try and keep the current as low as possible when tuning, less the 200 milliamps (.2) on the bottom scale, by doing this your tubes should last a long, long time.
Hope this help you.