There are two (basic) ways you can acquire a 27% stake in a company.
One is to buy 27% from existing shareholders, which means they cash in and the company gets no extra money.
The second is to subscribe for new additional shares, which means the extra money goes into the club. Provided the price is correct, the value of the club goes up but the existing shareholders have a smaller share of a bigger pie, and don't lose any value. This seems to be what happened with FSG and Red Bird Capital, but obviously the money there went in at the top and didn't necessarily trickle down to LFC (and probably didn't). For example, if the company is worth £100 with 100 shares in issue, you'd subscribe £37 for new shares, so your share would be 37/137 = 27%. The old shareholders have 73% of £137 = £100.
Of course, you could also do a bit of both (e.g. buy 20% and subscribe new money for extra shares to take you up to 27%).
The press quotes issued by West Ham say that "Daniel's involvement brings investment which strengthens the club's position and in turn will assist in the development of the club's key area of focus." This implies that at least part of this deal involves an injection of new money into the club. This will partly prop up any covid losses and also potentially give them capacity to spend. The details should become apparent over the next month or so as if there has been a new share issue then that will need to be registered with Companies House. Having said all that, the "brings investment" comment was made by Karren Brady. I met her at a Premier League meeting once and she wasn't the sharpest tool in the box, so she may have misrepresented the position.
The other thing to focus on is the shareholding itself. Most board / shareholder votes are carried by a simple majority but there are some issues where a >75% majority is required (these are called "special resolutions"). The shareholding of 27% doesn't give the new guy any positive control over the company, but it does give him enough votes to block some of the more fundamental shareholder matters (so some element of negative control). Whilst special resolutions are relatively rare and quite technical, having a 27% share does give a shareholder a fair amount of power and means Gold and Sullivan won't be able to use the club as their plaything if they want to.
It's also possible that this will be a pre-cursor to a full takeover at some point in the future (a la Moshiri / Usmanov), and I'd expect he'll have first refusal if the the other shareholders decide to sell up.
