What happens when you press Start
When you open a bot for the first time, Telegram shows a Start button instead of the usual message box. Pressing it sends the command /start to the bot. From the bot's side, this is the first sign that you exist. It now has a chat with you and can reply.
That is also why every bot needs a good answer to /start. It is the first thing the bot ever says to a person, and most people decide in that moment whether to keep the chat or close it.
Why a bot cannot message you first
Telegram does not let a bot start a conversation. A bot can only write to people who have pressed Start, and it stops being able to reach anyone who blocks it. This rule is what keeps Telegram bots from becoming a spam channel, and it shapes how businesses use them: the bot has to earn the first tap with a link, a button in a channel, or a QR code.
Start links with a parameter
A link to a bot can carry extra text after a start parameter, in the form of the bot's address followed by ?start= and a short code. When someone opens that link and presses Start, the bot receives the code with the /start command. Shops use it to know which post or partner a customer came from, or to open a specific product straight away. The person sees nothing unusual; the bot simply knows more about the first visit.
What a good first reply contains
Keep it short. Say what the bot does in one line, show the one or two actions people come for as buttons, and offer a way to change the language. For a shop, that usually means a button that opens the storefront. For a community bot, it means the rules and a way to join.
In BotLaunch, the shop bot answers /start with a greeting and a button that opens your storefront, and you can rewrite that greeting from the dashboard. The platform bot answers in the person's language and offers /lang to switch.
Other commands that sit next to /start
Most bots also answer /help, which lists what the bot can do. Telegram shows a bot's commands in a menu next to the message box, so people do not have to remember them.