Learn Turkish: Akşam menüsü masada duruyor. - The dinner menu is sitting on the table.

This is an indefinite noun compound. To combine two nouns like akşam (evening) and menü (menu) to mean 'evening menu', the first noun stays exactly as it is, and the second one takes a possessive suffix. Because menü ends in a vowel, it needs the buffer letter -s- before the vowel harmony ending -ü.

Does akşam mean 'dinner' or 'evening'?

akşam strictly means 'evening', but Turkish speakers frequently use it to refer to the evening meal. So akşam menüsü literally means 'evening menu', which is the natural way to say 'dinner menu'. You will also often see akşam yemeği used for 'dinner' (literally 'evening meal').

I thought duruyor means 'is stopping'. Why does it mean 'is sitting' here?

The verb durmak does mean 'to stop', but it is also used to mean 'to stand' or 'to remain'. When talking about inanimate objects placed somewhere, like a menu on a table, duruyor is the natural way to say it is sitting, resting, or located there.

Why is the suffix -da used on masada?