Step 1 :Define the sets $A$ and $B$ as $A=\{x \mid x<3\}$ and $B=\{x \mid x \geq 8\}$ respectively.
Step 2 :The union of two sets, denoted $A \cup B$, is the set of elements that are in $A$, or in $B$, or in both. In this case, the union of $A$ and $B$ would be the set of all real numbers less than 3 or greater than or equal to 8.
Step 3 :The intersection of two sets, denoted $A \cap B$, is the set of elements that are in both $A$ and $B$. In this case, since there are no real numbers that are both less than 3 and greater than or equal to 8, the intersection of $A$ and $B$ would be the empty set, denoted $\varnothing$.
Step 4 :In interval notation, the set of all real numbers less than 3 is represented as $(-\infty, 3)$, and the set of all real numbers greater than or equal to 8 is represented as $[8, \infty)$. The union of these two sets would be represented as $(-\infty, 3) \cup [8, \infty)$, and the intersection would be represented as $\varnothing$.
Step 5 :\(\boxed{A \cup B=(-\infty, 3) \cup [8, \infty)}\)
Step 6 :\(\boxed{A \cap B=\varnothing}\)