Contacts can typically be added in one of three ways:
They can text in your opt-in keyword(s). You can view opt-in keyword information from your Opt-in Keywords page.
They can sign-up via your sign-up page.
If you already have consent from people to send them messages, you can add them manually from your Control Panel under the Contacts tab, either one-by-one or by important a spreadsheet.
More advanced methods of adding contacts are via QR code and through integrations or API.
Opt-in keywords
Your account will come with at least one free opt-in "keyword." This is a word that people can text in to a particular number to be automatically added to your contact list.
For example, if your keyword was sale on the number 74121, people could send a text containing the word "sale" (no quotes) to 74121 and their number would automatically be added to your database.
You can view and edit your keyword(s) from the Opt-in Keywords tab on your dashboard.
Sign-up page
People can sign themselves up for your text alerts by going to a free online sign-up page that comes with your account.
You can edit information for your sign-up page under the Subscribers->Sign-Up Page tab on your control panel.
Adding manually
You can add contacts manually by clicking the "Add" button on the Subscribers->Manage Subscribers tab on your control panel.
If you have a list of multiple contacts that you want to add at once, you can set up a spreadsheet in the correct format and import it under Contacts->Import Contacts.