Along or alongside?

As a preposition, along means ‘in a line next to something long and thin’, e.g. a road, a path:

There were lots of shops along the main street.

I saw three different boats along the bank of the river.

We use along as an adverb with verbs of motion meaning ‘together with’:

Why don’t you come along with us to the party?

They said they’d bring the bikes along and we can ride to the swimming pool.

As a preposition, alongside means ‘close beside’, ‘next to’ or ‘together with’:

The trees alongside the fence have all been damaged by the wind. (near)

Put your bike alongside mine. (next to)

I find it difficult to cope with this illness alongside all my other problems. (together with)

We also use alongside as an adverb, meaning ‘along the side of’ or ‘next to’ something:

I parked my car in the drive and William parked his alongside.