Formal or informalHelp or assist
Everyday and neutral: works almost everywhere.
Can you help me carry these books?
Formal: offices, announcements, job letters.
Staff at the help desk will assist you.
Remember: Help works everywhere. Assist sounds official, as in announcements and job roles: "Teaching Assistant".
Short lessonFormal or informalWe speak differently to friends, teachers and officials. This change in style is called register.