mountain, mount an

Mountain or mountain means a large hill or elevation in the surface of the Earth--
This is the highest mountain in the state.
We will climb up the mountain, and have our lunch at the top.

Mount an or mount an means to install or set at an elevation ( mount ) one of something ( an )--
We can mount an automatic camera over the door--one that only works if someone steps on the mat.

Mount also means to stick to a background or on a slide--
This is the best way to mount an old photograph.

Mount also means to stage, as a play or military campaign, or to put in position for use, as a gun--
We will mount an assault on the enemy's position at dawn.
During the ceremony, we will mount an old cannon on the lawn of the Town Hall.

Mount also means to go up or climb, literally or figuratively--
To get upstairs, they had to mount an escalator that wasn't working.
You can mount an obstacle if you are determined enough.

Mount also means to get up on, as a horse or a platform--
He tried to mount an unfriendy horse, and it threw him.
They had to mount an old rickety platform; it shook with every step.

Now that you know that, you can say--
"To continue up the mountain, they had to mount an old set of log steps."

Note--"mountains" is the plural ( more than one ) of "mountain", meaning a large hill or elevation--
This chain of mountains reaches almost to the coast.
"Mounts an" is the third person singular ( he, she, it ) form of "mount an", meaning to install, climb, go up, or stage ( mount ) one of something ( an )--
When he mounts an old play, it's always popular.