Вот $5$ предложений с модальным глаголом can / can't:
$1$ "I can swim across the lake."
$2$ "She can speak three languages fluently."
$3$ "They can't come to the meeting because they're busy."
$4$ "Can you help me with this problem?"
$5$ "You can try restarting the computer to fix the issue."
Кратко: can — способность, разрешение или возможность; can't — отсутствие способности или запрет.