Orbot

Tor is both software and an open network that helps you defend against network
surveillance that threatens personal freedom and privacy, confidential business
activities and relationships.

Orbot allows access to Tor by accessing a local SOCKS or HTTP proxy.
On a rooted device, the proxying can be completely transparent
i.e. the app that accesses the network need not be aware of the
proxy's existence; you can choose which apps go via the proxy in the
settings.

If you don't have root access, there are some apps that are designed to work
closely with tor or allow proxied connections: https://f-droid.org/packages/acr.browser.lightning and
https://f-droid.org/packages/org.mariotaku.twidere. There is also a proxy configurator addon for Firefox
called ProxyMob (not yet
available from the Mozilla addon site).