First, let me explain THE ONLY WAY to make a server without any third-party application (pocketmine, leet, etc.). Port forwarding is the secret. What it does is with the correct IP address of a device is set up with the real IP of your router, you can use a specific port to forward players to your world. That's actually how PocketMine, Leet, and other great payed server apps do it, and then add plugins.
Second, the server acts as a LAN server (playing with someone on the same WiFi). Except, in this case, you can let people from AROUND THE WORLD to join you.
Third, if the password to your router settings is password, you'll have to trust the people you give your IP to. 'Cause when you give them the IP, they can get into your router and mess things up, such as: changing the password, blocking your devices from joining, etc. If not, then you'll be okay.
Step 1: Getting to Know Your IPs
To start off, simply go to the settings app of your device (not computer, you won't need it anyway). Go to the WiFi settings, then click on your connected internet thingy to open the list of data. Memorize or write down the IP of your device. This device you are on is the one that people will connect to. So make sure you have MCPE on it.
Next, memorize or write down the router's IP. It should look similar to your IP (192.168.1.# or 10.0.0.#, etc).
Step 2: Into the Router Settings/Port Forwarding
Now, search up the router's IP address. Make sure there are no mistakes. You should then see a login page. To log in, find the router in your house, which would look like a box with fluctuating lights. Look around it until you find a username and password. If you don't,... I don't know what you'll have to do. Maybe ask your parents. NOTE: if you have a default admin/password login, then you'll need to trust the people you give the IP to. Use the login and log in.
Find Port Forwarding. It's probably in the advanced settings. If not, just keep looking for it. Now, add a new rule. For the IP address, put in the one of your device. For the port, you'll need both TCP and UDP (start and end) ports. Use the default Minecraft PE port, 19132. For frontier, select custom ports. For Verizon, ignore what frontier did. Finally, save the rule. Congrats, you've set up the server! Now, you need the right info for your friends to join.
Step 3: The REAL IP Address
For the last step, search up ipchicken.com. This is the IP that your router uses to connect you to the Internet. By now, I've figured out that there are two types of IP: ones of devices, and ones of links.
Anyways, share this IP with your friends so they can join you when you are on at your house! Just make sure they use the default port for Minecraft PE, 19132.
Now that's that, you can ask me any questions in the comments down below. Thanks!