快速答案
participar 表示参与活动；assistir 表示作为观众或观察者观看。
可靠的方法是先判断这个词在句子里的功能，再翻译。
每个词的作用
participar
to participate or take part
Use participar for being actively involved in an event, group, or activity.
assistir
to watch or attend
Use assistir for being present mainly as a viewer or audience member.
如何选择
- participar: Choose participar if the sentence points to being actively involved in an event, group, or activity.
- assistir: Choose assistir if the sentence points to being present mainly as a viewer or audience member.
例句
Participei da reunião.
I took part in the meeting.
Assisti à palestra pela internet.
I watched the talk online.
常见误区
Being present does not prove participation. In careful usage, assistir meaning watch takes a: assistir à palestra.
放到语境中练习
从你的真实生活中选一个句子，写两遍：一次用 participar，一次用 assistir。如果两个版本都可以，说明意思怎样变化。