You can use the subscribe form code. Go to your desired subscriber list, then click the 'Subscribe form' button at the top right to get the subscribe form code.
Paste the code into your sidebar widget. Optionally, if you want to redirect the user to a specific URL after they subscribe, you can set this in the list settings. You'll also see many other options in list settings.
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You can use the subscribe form code. Go to your desired subscriber list, then click the 'Subscribe form' button at the top right to get the subscribe form code.
Paste the code into your sidebar widget. Optionally, if you want to redirect the user to a specific URL after they subscribe, you can set this in the list settings. You'll also see many other options in list settings.