You can set Proxy IP address, port, and authentication information in Tor Browser's Network Settings. If you're using Tor another way, check out the HTTPProxy and HTTPSProxy config options in the manual page, and modify your torrc file accordingly. You will need an HTTP proxy for doing GET requests to fetch the Tor directory, and you will need an HTTPS proxy for doing CONNECT requests to get to Tor relays. (It's fine if they're the same proxy.) Tor also recognizes the torrc options Socks4Proxy and Socks5Proxy.

Also, read up on the HTTPProxyAuthenticator and HTTPSProxyAuthenticator options if your proxy requires auth. We only support basic auth currently, but if you need NTLM authentication, you may find this post in the archives useful.

Si tus servidores proxy solo te permiten conectar a ciertos puertos, lee la página clientes detrás de un cortafuegos para saber como restringir los puertos a los que Tor intentará conectarse.