The most basic instruction is the beginning and end. To begin a program, place down a stone block. Then, whilst looking at that block, run the command /trigger fungecraft.play. This should start the program 1 block south of the stone. The execution will continue south until it hits a directional operator, or bedrock, which terminates the program.
The directional operators are magenta glazed terracotta, which looks like an arrow, and when the program pointer reaches one of them, it continues in the direction the arrow is pointing.
Then there are the mathematical operations.
There is addition, which is represented by an oxidised cut copper block,
Subtraction, which is a jukebox,
Multiplication, which is a honeycomb block,
Division, reperesnted by light blue glazed terracotta,
And modulo, nether quartz ore.
Each of these pops two values from the stack, a then b, and pushes back on the operation calculated with b and a (e.g. if the stack had a 2 then a 3, then you put a minus operation, it would pop 3 then 2 and push 2 - 3)
Chart for the different blocks in the MSBE (Minecraft standard block encoding (Really just the Fungecraft standard encoding)):
0: Black Wool
1: gray Wool
2: Brown Wool
3: Light gray Wool
4: White Wool
5: Red Wool
6: Orange Wool
7: Yellow Wool
8: Green Wool
9: Lime Wool
10: Cyan Wool
11: Light Blue Wool
12: Blue Wool
13: Purple Wool
14: Magenta Wool
15: Pink Wool
16: Black Concrete Powder
17: gray Concrete Powder
18: Brown Concrete Powder
19: Light gray Concrete Powder
20: White Concrete Powder
21: Red Concrete Powder
22: Orange Concrete Powder
23: Yellow Concrete Powder
24: green Concrete Powder
25: Lime Concrete Powder
26: Cyan Concrete Powder
27: Light Blue Concrete Powder
28: Blue Concrete Powder
29: Purple Concrete Powder
30: Magenta Concrete Powder
31: Pink Concrete Powder
32: Air
33: Bamboo
34: Black Concrete
35: gray Concrete
36: Lava Cauldron
37: Nether Quartz Ore
38: Observer
39: Brown Concrete
40: Light gray Concrete
41: White Concrete
42: Honeycomb Block
43: Oxidized Cut Copper
44: Oak Sign
45: Jukebox
46: Warped Sign
47: Light Blue glazed Terracotta
48: Chest
49: Red Concrete
50: Orange Concrete
51: Yellow Concrete
52: green Concrete
53: Lime Concrete
54: Cyan Concrete
55: Light Blue Concrete
56: Blue Concrete
57: Purple Concrete
58: Dispenser
59: Magenta Concrete
60: Magenta glazed Terracotta (facing north)
61: Pink Concrete
62: Magenta glazed Terracotta (facing south)
63: Dropper
64: Bedrock
65: Stone
66: Cobblestone
67: Deepslate
68: Cobbled Deepslate
69: Coal Ore
70: Deepslate Coal Ore
71: Coal Block
72: Copper Ore
73: Deepslate Copper Ore
74: Raw Copper Block
75: Copper Block
76: Iron Ore
77: Deepslate Iron Ore
78: Raw Iron Block
79: Iron Block
80: Lapis Ore
81: Deepslate Lapis Ore
82: Lapis Block
83: Redstone Ore
84: Deepslate Redstone Ore
85: Redstone Block
86: Emerald Ore
87: Deepslate Emerald Ore
88: Emerald Block
89: Diamond Ore
90: Deepslate Diamond Ore
91: Diamond Block
92: Piston
93: Ancient Debris
94: Magenta glazed Terracotta (facing east)
95: Repeater (facing south)
96: Comparator
97: Netherite Block
98: Black Terracotta
99: gray Terracotta
100: Brown Terracotta
101: Light gray Terracotta
102: White Terracotta
103: Note Block
104: Red Terracotta
105: Orange Terracotta
106: Yellow Terracotta
107: green Terracotta
108: Lime Terracotta
109: Cyan Terracotta
110: Light Blue Terracotta
111: Blue Terracotta
112: Sticky Piston
113: Purple Terracotta
114: Magenta Terracotta
115: Pink Terracotta
116: Black Carpet
117: gray Carpet
118: Magenta glazed Terracotta (facing west)
119: Brown Carpet
120: Light gray Carpet
121: White Carpet
122: Red Carpet
123: Orange Carpet
124: Yellow Carpet
125: Repeater (facing west)
126: Lectern
