May peace be with you.
'Manasik' is a plural phrase of the word 'mansak' which means a holy rite (religious ceremony / ritual / devotional act etc). Different rites were performed by different nations. (22:34, 22:67).
'Sha'air’ (plural 'shi'arah) means waymark, a symbol or an indication. In verse 2:158 (as in 5:2, 22:32 and 22:36), the references are to God's indications / waymarks / symbols etc.
Sometimes a rite (mansak) can be performed around a shi'arah of God (symbol of God) as in verse 2:158.
I hope that helps, God willing.
Joseph.