A: in the drawing above
These measurements mark the footings.
In this case the top line shows the overall measurement of the building width, the middle line shows the overall measurement of the building recesses and the bottom line shows where the concrete blocks go.
B: in the drawing above
These lines show where the block work and footings go. The continuous straight lines mark where the 200mm (8") concrete blocks go, and the continuous dotted lines mark where the 300mm (12") wide footings go, 50mm (2") each side of the concrete block line.
C: in the drawing above
"300x300 (12"x 12") perimeter footing with 2 D12 rods (2 #4 rebar) and D10 (#3 rebar) link/starters at 600crs (24" O.C.) lap 600 (24") into slab"
This means the footing will be continuous and 300mm (12") wide and 300mm (12") deep. The dotted lines on the plan marks the outline of the footing. Two D12 rods (#4 rebar) run the length of the footing and are tied with tie wire to D10 (#3 rebar) link/starters spaced every 600mm (24") apart. The D10 (#3 rebar) link/starters must lap into the concrete slab at least 600mm (24"). For a better understanding have a look at the cross-section plan
NOTE: D12 rod means deformed steel 12mm thick. That is metric. The equivalent in imperial (USA) is #4 rebar, which is 1/2" thick.
D: in the drawing above
"Drill & epoxy 700 (28") long D12 (#4 rebar) starters 100mm (4") into existing slab and foundations at 600crs (24" O.C.)."
This means drill 12mm (1/2") holes at least 100mm (4") deep into the side of the existing concrete slab every 600mm (24") apart. Glue into the holes (with epoxy) 700mm (28") long pieces of deformed 12mm (1/2") thick steel. This ties the new concrete footings and concrete slab to the existing.
Steel rods (D12, D10 etc) can be purchased from most major building suppliers and comes in 6 metres lengths. Steel benders and cutters can be hired from most hire firms.
In USA steel rods are called rebars and a D12 would be the same as #4 rebar which is 1/2" thick. #2=1/4", #3=3/8, #4=1/2" and so on in increments of 1/8" for every #1.