If you don't instruct the search engine, it will pick the first chunks of text on your website to display on the search result page. You can, from a marketing perspective, do way better by defining yourself a powerfull text. This should convince the reader of the SERP page to select your website as the one to visit.
This paragraph will discuss the methods to use to achieve this.

Meta Tag

Meta text are chunks of text you will see back in the search results. The title and meta description

The tag title is one of the key chunks of text relevant in the context of search engine optimization. It’s the text returned on the SERP (Search Engine Result Page). You will not find this piece of text back on your website, although it might be displayed in the window title of your browser:

Tag

• Max length 65 characters
• Call-to-action or ask a question
• Put your main keyword or keyword phrase upfront
• Select a branding method (don’t start with the company name)

Remember that having a good SERP position is not sufficient. If the text shown in the search result is not attractive to improve the CTR (Click Through Rate), you have an issue. So think twice when writing this text...

Meta Description

paragraph of the HTML
Not visible on your website, but visible on the SERP

• Will appear as a chunk of text underneath the Google title tag (snippet)

Good practice is to provide the text for the meta description in the HTML source code for your page. If you provide this, then this text will be displayed underneath the title tag for your search result on the SERP. If you don’t provide this, the search engine will still provide a chunk of text.

In conclusion, you can state that meta descriptions are important for searchers, search engines and webmasters.

Tips for writing a powerfull Meta Description

<150 characters

• When longer, will get truncated

Focus on a better CTR (click through rate)

• Meta descriptions don’t have a function in getting a better SERP ranking. You need to use them to convince people to click through and visit your website. So make sure you pull there attention and have a convincing pitch. If your description is the most compelling one, they might click on your search result, event though you might be ranked a couple of places down on the SERP page.

But do use some keywords

• Using keywords here doesn’t count for your position on the SERP. But people do expect to see those things hey where searching for mentioned in your text. Google will boldface the keywords used in the query that appear in your text. .

Type of queries, descriptions

• Information can have different appearances. This is also visible through the query. The 4 most frequent types are::

1. Navigating query: ‘looking for information about Apple’. The Apple home page could be a good search result here.
2. Informative queries: ‘Name actor A beautiful mind’
3. Commercial queries: ‘SEO consultant’
4. Transactional query: vb. ‘Plumber Brussels’

You don’t need to use full blown sentences.

• Short and readable, having some words implied, is often better
• You can add some data. E.g. a book could mention author, editor and price.

Where to place your keywords ?

What’s the usage difference then between a tag title and a h1 header ? The later one pulls the attention of the reader, and helps both end-user and search engine to get some structure. The tag title is not visible on your website, only in the search results. You should succeed in convincing the searcher to click your result to visit your website.