Bridges allow you to use other external accounts through your Matrix Homeserver. So with the Discord Puppet Bridge[1] I am using I can log into my Discord account from Matrix and handle all my Discord DMs and group chats using a Matrix client. So yes, bridges allow you to use Matrix for all your other chat applications.
The general workflow is after you install bridges that you configure your bridge to your existing account on the other platform. So for Signal, you open a chat with the Signal Bridge bot and issue a command to link to your account and then it walks through that process. Once the bridge is configured with your external account any new DMs and group chats from those external accounts will show up as DMs in Matrix.
The general workflow is after you install bridges that you configure your bridge to your existing account on the other platform. So for Signal, you open a chat with the Signal Bridge bot and issue a command to link to your account and then it walks through that process. Once the bridge is configured with your external account any new DMs and group chats from those external accounts will show up as DMs in Matrix.
Hopefully that makes sense! :)
[1] https://gitlab.com/mx-puppet/discord/mx-puppet-discord