If you assist someone, you give them the help they need. For example, a nurse can assist a doctor, a guide can assist someone who needs information, or you can assist someone who has fallen by picking them up.
1. Two of his men assisted the midwife and the baby was born.
2. I enclose a simple map that may assist you.
3. He assisted her to the stool.
You use attend to talk about being present at an event such as a class or a meeting. You do not use assist in this way.
4. Each day he walked several miles to attend his lectures.
5. I stopped off in London to attend a conference.