INSTRUCTION FORMAT FOR PROTECTED MODE, REAL-ADDRESS MODE, AND VIRTUAL-8086 MODE
The Intel 64 and IA-32 architectures instruction encodings are subsets of the format shown in Figure 2-1. Instructions consist of optional instruction prefixes (in any order), primary opcode bytes (up to three bytes), an addressing-form specifier (if required) consisting of the ModR/M byte and sometimes the SIB (Scale-Index-Base) byte, a displacement (if required), and an immediate data field (if required).

Source: Intel^® 64 and IA-32 Architectures Software Developer's Manual, June, 2013

Except for the opcode, all of these parts are optional.
They are only present when the particular instruction requires them.

Opcodes can be 1, 2 or 3 bytes.
There can be 1-4 Operands
Terms:

ModR/M - Byte which  tells the processor which registers or memory locations
         to use as the instruction's operands.
SIB - Scale-Index-Base