How to use selected text in apple script? I want to add text before and after it

Idea: I select text, and it gets replaced with <sometag>selected text</sometag>.

Code:

on run {input, parameters}

tell application "System Events" to keystroke "<tag>[what should go here]</tag>"

    return input
end run

Briefly, have your workflow accept Text from Any Application and check the box that is labelled something like Output Replaces Selection.

Then, all you need is a single Execute AppleScript action, in which you should replace any example code with this:

on run {input as text}
    return ["<sometag>", input, "</sometag>"] as text
end run

which can also be written like this:

on run {input as text}
    return "<sometag>" & input & "</sometag>"
end run

The workflow would need to be saved as a Service or Quick Action, and then be activated in System Preferences where other "Services" are listed.