Merkha is a very common note. It has lots of uses and can come before a bunch of notes. But mostly, it comes before a tip’ha or a sof pasuk.
Merkha is always connected to the word that follows, which can help you figure out the meaning of the sentence. Here’s a great example from our parashah.
לְהַעֲלֹ֥ת נֵ֖ר תָּמִֽיד׃
To regularly set up a lamp
The version on the left is what actually appears in our parashah. The merkha connects the word לְהַעֲלֹת (le-ha’alot, to set up) with the word נֵר (ner, lamp). The act is setting up a lamp, and that action needs to be done regularly, like once or twice a day.
The version on the right would mean something different. Here, the merkha would connect the word ner to the word תָּמִיד (tamid, regularly). That would mean the act is setting something up once, and the thing being set up is a lamp that burns regularly on its own.