Consider the reaction.
H
CH3
$C=C$ + H-Br: $\longrightarrow$ H-C-C-CH3
H H H H Br:
Add curved arrows for the first step.
Draw both the organic and inorganic intermediate species. Include nonbonding electrons and charges, where applicable. Include hydrogen atoms.
H
H
C=C
CH3
H
H
H-Br:
$\longrightarrow$