Learn Turkish: Sebzeleri uzun süre kaynatmak lazım, yani sabırlı olmak gerekli. - It is necessary to boil the vegetables for a long time, meaning it is necessary to be patient.

Here, yani means "in other words" or "meaning that." It connects two statements where the second draws a logical conclusion or summarizes the first. Şöyle ki ("namely" or "which is to say") wouldn't work as well here. You use şöyle ki when you are about to launch into a deeper explanation or list the specific details of what you just said, rather than just offering a quick, logical summary.

The sentence uses both lazım and gerekli for "necessary." Is there a difference between them?

No, they are essentially interchangeable in this context. Lazım is an Arabic loanword, while gerekli is a native Turkish word. Using both in this sentence is simply a stylistic choice to avoid repeating the same word twice, much like alternating between "necessary" and "required" in English.

Why is the verb kaynatmak used instead of just kaynamak?

Kaynamak is intransitive; it describes the action of the item itself boiling (e.g., "the water boils"). Because you are actively boiling something else (the vegetables), you need the causative suffix -t to make it kaynatmak (literally "to make boil"). This is also why "the vegetables" takes the accusative case ending to become the direct object: sebzeleri.

Why aren't there any personal endings on the verbs, like kaynatmam lazım?