How do non-standard transactions get created, broadcast and mined? Can someone explain how this transaction was validated, broadcasted and mined? 

When i looked at the scriptsig it only had the hex value for OP_True.

https://blockchain.info/tx/91c8b08f305d895d6bc8f43bbdd36dcbc7f1d998e3df5e8f13dd9cdeebf15cb5?show_adv=true
Also how can i create a transaction like this and have it broadcasted and mined?
Normally, non standard transactions would be rejected by P2P nodes (but would still be mineable by miners directly since this is just a policy rule).

P2SH addresses do not disclose the script they hash until they are first spent from. So you can send BTC to any script (valid or not) using P2SH addresses. Standardness rules are not imposed on P2SH input scripts, they just have to respect the protocol rules (size, use enabled opcodes, etc...).

To create your own scripts, you can use this question as a starting point.