There are 2 ways to share the link of your Channel in Telegram, so users can either read your public channel or be requested to join the channel via the join chat link.
If you just share your Channel's link (Use @YourChannelName inside the Telegram, or Telegram.me/YourChannelName outside the Telegram), users will be able to read the content of your public channel by clicking/tapping on that link and there is a Join button on the bottom of the screen letting them join your channel.
But there is another type of sharing Channel's link in Telegram, which is called JoinChat Link and asks the user whether he/she want to join a specific channel as soon as clicking the invite link, without showing the content of that channel. In other words, it makes you join the channel in Telegram to read its posts, which is a very good idea to increase the number of your channel's subscribers.
Well, to create a Join Chat link for a Channel in Telegram you need to do as follows:
1. Make sure you are using the latest version of Telegram on your device (The instructions, is a little different in the older versions)
2. Open the Telegram app and then open your Public Channel which you want to create the JoinChat link for
3. Tap the Channel's Name on the top to open the Channel's details
4. Tap the 3-dot icon on the top right of the screen, and then hit the Edit button (You have to be the admin of this Channel)
5. Tap the Channel Type option
6. Change the channel from Public to Private (don't worry, you can change it again to Public without losing anything)
7. Now the Invite link appears on the screen, which is the Join Chat link for the Channel in Telegram we were looking for
8. Just touch the invite link to copy it to the clipboard and then switch the channel back to Public.