What this suffix does
The suffix -ship creates nouns that name relationships between people, skills or conditions. From "friend" you get "friendship"; from "leader" you get "leadership"; from "partner" you get "partnership".
It is one of the oldest suffixes in English and appears in very high-frequency vocabulary across professional, personal and social contexts.
Three main groups
1. Personal relationships: friendship, partnership, companionship.
2. Skills and roles: leadership, craftsmanship, sportsmanship.
3. Conditions and states: hardship, citizenship, membership, ownership.
The common thread is that -ship always names something abstract that exists between people or that defines a position or condition.
No single Spanish equivalent
Unlike -ism or -ity, -ship does not map to a fixed Spanish ending. It depends on the word.
friendship = amistad
leadership = liderazgo
citizenship = ciudadanía
membership = membresía
hardship = dificultad
The most effective strategy: learn the most common -ship words directly as vocabulary, without looking for a translation pattern.