If I understand correctly, something like this:

Let's say you have hosts A and B.

Doing this from A:

    ssh -R 1080 B

will start a SOCKS5 proxy on A, to which you can connect on B through port 1080 that's being forwarded there. So your web client running on B will use traffic proxied through A while connecting to 1080 on localhost.

> Does it try to autodetect whether you're speaking SOCKS to it

I think it just uses SOCKS5 out of the box if you don't specify the host for -R. According to the man page for -R:

    if no explicit destination was specified, ssh will act
    as a SOCKS 4/5 proxy and forward connections to the
    destinations requested by the remote SOCKS client.

If you don't specify a destination for -R it will work in SOCKS mode.

> ssh -R 8080:localhost:8080 #Port forward

vs

> ssh -R 8080 #SOCKS