How would I even go about starting investing using this? Let's say I have a trading212 account or similar? Where do you even start? Do you have a "how to get started page" assuming someone knows little about investing.
The easiest way to use Grizzly Bulls is to hold VOO in any brokerage account, sell it when the model generates a sell signal, and then rebuy it when the model generates the next buy signal. A slightly more advanced but more tax efficient approach would be to open a margin account with futures trading permissions and sell S&P 500 Futures (ES or MES) of equal value to your VOO during sell signals, then repurchase the contracts you sold during the next buy signal. With this method, I've found you can usually reduce your overall tax burden to less than 15% and you'll only owe taxes on the net result of your futures trading.
The only way to really drop below your maintenance margin is if you are either leveraged long (i.e. more than 100% long) or short (i.e. less than 0% long), and the market moves significantly against you. In that scenario, your broker will automatically start liquidating some of your positions.
However, this does mean that you'd need to open an equivalent position in the next quarter's contract to maintain your hedge, if one was open, at expiration time which is regular trading hours opening time on the third Friday of expiration month.