Summarize the following:
You need to have a Twitter account to create this widget.   You will arrive to a page titled “Create a user widget.”. On the new tab, beneath the “Configuration” heading, in the search query, put your hashtag. (e.g. #wikiHow). Select whether or not you’d like to only display “Top Tweets,” if you want the widget to be in “Safe Search Mode,” and whether you want to “Auto-expand photos” by clicking the corresponding checkboxes. Select the height in pixels you’d like the widget to be. By default, it’s 600px. The next option down whether you want the contrast of the widget to be light (dark text on light background) or dark (light text on dark background). Pick what color you’d like links to be. You can either use an HTML color, or select from a color picker.  On the next page, beneath your preview, is the HTML code for your widget. Copy it to your clipboard and paste it to your website.

Summary:
Log in to your Twitter account. Go to https://twitter.com/settings/widgets  Click the “Create New” button at the top right of the page. Click the “Search” tab. Input your hashtag. Configure the settings. Click “Create Widget” at the bottom. Copy and paste to website.