Note: According to the Quickstart guide Weechat-Android is not a chat-program, it is only a UI for a chat program running on your server:
Weechat-Android is a relay client, that is it's not a standalone
client, but one that connects to your copy of WeeChat running on your
server. You can connect the two in a number of ways, listed below.
Therefore if you just install the app on your phone it is not usable. You still need an own server on the Internet where your Weechat program is executed.
You can connect to freenode by pointing your IRC client at
chat.freenode.net on ports 6665-6667 and 8000-8002 for plain-text
connections, or ports 6697, 7000 and 7070 for TLS-encrypted
Connect to chat.freenode.net
Alternatively there is a Weechat how-to for setting the correct server: https://freenode.net/kb/answer/weechat
/server add freenode chat.freenode.net/6697 -ssl
/set irc.server.freenode.sasl_mechanism PLAIN
/set irc.server.freenode.sasl_username <nickname>
/set irc.server.freenode.sasl_password <password>