Learn Turkish: Karanlıkta sığınağa kadar sürünemezdik. - We couldn't have crawled to the shelter in the dark.

It combines the inability suffix, the negative aorist, and the past tense. Let's break down sürün-eme-z-di-k: sürün (crawl), -eme (inability - "unable to"), -z (negative aorist marker), -di (past tense), and -k ("we"). The negative aorist in the past (-z-di) translates to "would not", and attaching the inability suffix makes it "would not be able to" or "couldn't have".

What is the difference between saying sürünemezdik and sürünemedik here?

Sürünemedik uses the simple past tense and states a fact: "we couldn't crawl" (we tried, but failed). Sürünemezdik is counterfactual: "we couldn't have crawled" or "we wouldn't have been able to crawl". It implies a hypothetical situation where crawling was impossible, so you likely didn't even attempt it.

Why does the word for shelter (sığınak) change to sığınağa?

The postposition kadar (up to / as far as / until) requires the noun before it to take the dative case (direction towards). When you add the dative suffix -a to sığınak, the hard k at the end of the word undergoes consonant mutation and softens into a ğ, resulting in sığınağa kadar.

Is the verb sürünmek (to crawl) related to sürmek (to drive)?

Yes, they share the same root. While sürmek often means "to drive," it also means "to rub" or "to drag." The -ün suffix makes it reflexive, so sürünmek literally means "to drag or rub oneself along," which is how Turkish expresses the act of crawling or creeping.