You do not need to know everything before attending a Dharma Assembly
You may follow the practice as guided during the Dharma Assembly. If you are unfamiliar with a particular mantra, mudra, or practice, you may observe and learn.
The exact sequence can vary according to the particular Dharma practice, so don't present this as the mandatory order of every Dharma Assembly. Official TBS sadhana materials show different practices with their respective procedures.
Invocation
敬請諸佛菩薩、根本上師及護法等。
Great Homage
大禮拜／大供養等，以恭敬心禮敬根本上師、諸佛、菩薩及護法。
Mantra Recitation
持誦咒語。
Mudra and Visualization
結手印及觀想。
Sutra Recitation
誦念佛經。
Samadhi
入三摩地。
Dedication of Merit
迴向功德。