There are two way of using hashtags on LinkedIn

(1) Following hashtags

You follow few hashtags to receive specific content on your news feed along with the regular content and participate in the relevant discussions. For example if you follow #entrepreneurs so LinkedIn algorithm will show you the post related to this hashtag and this will give you an opportunity to participate in discussion where you can grow your profile visibility among your target audience. If you use #career #jobsearch #interview etc you will reach people who must be looking for job change, corporate professionals, students who are searching job.

How to follow relevant hashtags?

Go to Homepage>click on My network and the will show you following window > Click on Hashtags> then click on "follow fresh perspectives" to follow new hashtags of your choice

You may follow as many related to your business but 15-20 would be sufficient. I am currently following 9 hashtags.