Save an entry with tags I have a project that the user choose a tag (tags are already created) and save the information.

I try save a entry which has a tag field, all the stuff saves, but the tags don't.  I try search information about that, but any where have a solution or the solution doesn't work.

I try entry form.
Hard to know without seeing some template code, but the syntax for saving existing tags on a front-end entry form looks like this:

&lt;select multiple name="fields[fieldHandle][]"&gt;
    &lt;option value="13"&gt;Tag Name One&lt;/option&gt;
    &lt;option value="42"&gt;Tag Name Two&lt;/option&gt;
    &lt;option value="144"&gt;Tag Name Three&lt;/option&gt;
&lt;/select&gt;


Replace fieldHandle with the actual handle of your Tags field and 13, 42 and 144 with the actual Tag IDs.

There's a great list of examples for what front-end inputs need to look like for Craft fields here you might find useful: https://straightupcraft.com/articles/craft-cms-field-guide-twig?view=input