Here is an example using the paragraph <p> tag:

What you type in:
line1
<p>
line2
</p>

What you see on your page:
line1

line2

As you can see, there is a complete line of space between line1 and line2.

Here is an example using the line break tag <br>:

What you type in:
line1
<br>
line2

What you see on your page:
line1
line2

As you can see, there is no space between line1 and line2. By including the <br> tag, line2 is placed on the line right below line1.

Here is an example of using the space &nbsp; tag:

What you type in (this is three in a row):
line1
&nbsp;&nbsp;&nbsp;
line2

What you see on your page:
line1   line2

As you can see, we used three &nbsp; tags in a row. This is because each &nbsp; tag creates only one space.