Learn Turkish: Eşyalarımın birkaçı sıradanlaştı, bu yüzden onları bağışladım. - A few of my belongings became ordinary, so I donated them.

It comes from the adjective sıradan (ordinary), which is actually formed from sıra (row/line) + the ablative suffix -dan ('from the row' = ordinary). The suffix -laş (or -leş) is added to adjectives or nouns to mean 'to become [that adjective/noun]'. Therefore, sıradanlaşmak means 'to become ordinary'. The -tı at the end is the past tense suffix.

Why use the structure eşyalarımın birkaçı instead of just saying birkaç eşyam?

While birkaç eşyam simply means 'a few belongings of mine', eşyalarımın birkaçı uses a genitive-possessive construction to mean 'a few OF my belongings'. This creates a partitive meaning, emphasizing that you are singling out a specific subset from the larger, definite group of all your things.

In the verb bağışladım, is the -la suffix related to the -laş suffix we just learned?

They are similar in that both turn nouns or adjectives into verbs, but their functions differ. The -la (or -le) suffix creates an active or transitive verb from a noun, turning bağış (a donation) into bağışlamak (to donate). The -laş suffix specifically indicates a change of state or 'becoming' something, as in sıradanlaşmak.

Since 'a few of my belongings' refers to multiple items, why doesn't sıradanlaştı have the plural suffix -lar?