Hashtags allow you to group your content to a specific category, meaning that when a Twitter user searches for a category, if your Tweet has that searched for hashtag within it, your Tweet will be displayed to them no matter where they are in the world, whether they are following you or not.
If you are a small online store or an ecommerce business looking to advertise your brand to a wide audience, hashtags are a great way to get your content seen by people who you may not have been able to reach through other marketing methods. What's more, the fact that these people are using this hashtag means that they may already be interested in the various products or service your business provides.
There is no limit on what you can have as a hashtag. However, you need to remember that if the hashtag is really obscure, the likelihood is that no one else will be using it, which means that no one will see your Tweet through the hashtag. A good place to start when selecting hashtags for your Tweets, is to simply use that hashtag that relates to what it is your ecommerce store sells. For example, if you sell electronic goods, use the hashtag "#electronics" on your Tweets.
There are a number of other popular hashtags that small businesses should look to use to help improve their identity and gain followers. These hashtags include "#ecommerce," "#SMEs" and "#business." These hastags are generally popular and will result in people outside your followers being able to see your related tweets.