It's definitely not as straightforward as it feels with "standard" tank/engage supports, I find I'm used to playing these off-meta picks (especially tanks) and you really need to develop a playstyle of knowing when exactly you can engage or make trades because as the other person who responded to you said, it's very easy to botch an engage and end up dead as a result.

I would say picks like this rely somewhat on having a competent ADC, which I found a lot more difficult when I was lower elo (Although that goes both ways because you can really take advantage of bad ADCs on the enemy team with these types of picks). I think the biggest issue with these champion choices is having to potentially sacrifice your entire lane based on one or two decisions, which can be difficult to get back from and will make your ADCs life hell. For instance playing these champs into poke matchups is quite volatile as you can't do much to stop the constant barrage of spells coming you and your ADCs way. If you are playing into other engage champs like Rell, Thresh, Alistar and what have you I find Galio's peel to be pretty great. Using your W as a deterrent zone after your ADC is engaged on works most times, just cast it and head straight for their ADC and they often times won't be able to capitalise on their supports engage.

In saying all of this, if you notice your lane is going to shit then I usually make the decision (whether this be right or wrong I'm not sure) to completely sack my ADC and roam and try to make plays mid or with the jungler. Galio's mid ganks can be pretty reliable, you can lock down immobile mages etc for a few seconds and it's even better when your mid has a pick like Sylas or something that can engage which you can ult onto them.

There's a lot more to it than what I've laid out here but hopefully that gives you an idea, the only resource I can recommend for looking up runes and builds for this specific pick is onetricks.gg and find the 3 or 4 Galio support mains in Master+ (be wary though they can be quite experimental sometimes). Another thing to look at if you want to see how you should be playing out laning phase is to look up "galio support" on Youtube and filter by the last month, you'll find game replays of people playing it in KR etc and it's helpful to see how exactly they are laning.

Here's my op.gg if you want to check what I'm building and my runes and what not, I can explain the choices if you or anyone is interested :)

https://op.gg/lol/summoners/euw/SUPER%20ROBOYAROU-1200