You might do well to find an FC and party with them until you get a better grasp of dps/healing. But its going to be rough fo ryou for a while if this is your first toon for a few reasons:

1) Veteran players do dungeons to get creation and the like, and are looking for fast clears. Healers, being crucial to dungeon clearing along with Tanks, will get an extra serving of salt if theyre not geared or underskilled.
2) You are going to be by default 'undergeared' for a while. While you may have the appropriate ilvl for dungeons, you wont have the 'max' stats that would be afforded to you if you were 70 in 340 gear. The dungeon sync lowers your stats by a certain rate, so being geared in 340 gear will serve you better in lower content thatn being in 260 or 130 gear. As a result, youre going to struggle harder to be a healer in a dungeon where tanks are speed pulling and pulling huge huge mobs.
3) A lot of tanks and DPS are 'bad'. This is a bit more controversial, but the truth is a lot of tanks and DPS are not great at the job they are playing. SOME ARE, yes, particularly if they main that class and know the ins and outs. But the chances are youll either end up with people who dont Main 'tanks' or DPS who are playing DPS that theyre not accustomed too. This is going to result in either slow kill times (which will end up with you running out of mana) or tanks who take to much damage because theyre not properly using cooldowns to mitigate damage and are pulling TO much. Mixed with the previous ones, they tend to assume its YOUR fault cause theyre to used to getting good healers who are geared and know how to babysit bad tanks.

I know you get a lot of salt, but if you still want to give the game a good try, then yeah, I recommend trying to find a server with an FC willing to pull you in and run things with you. Also, posting here helps, and there are discord groups dedicated to learning classes and things, so joining them and talking with the veterans there is a big deal as most of them are pretty damn friendly.

Lastly, this is a big deal that a lot of beginning healers dont undestand but...

Fight Mechanics>Class Mechanics> DPS. Dead Healers heal no one. And if youre not familiar with your class, DPSing is a moot point. So while people may berate you for 'not dpsing' tell them to screw off. Get a solid understanding of how your class works from a support perspective before really worrying about DPS. It will serve you much more long term to be a amazing healer who never dies to mechanics but eh DPS, than to be a so-so healer with ok dps who dies half the time to cleaves or AoE. And in dungeons, just go ahead and let teh Tank know youre not super geared healer and to try to take it easy on pulls if possible. Some people will try to kick you, yes, but most tanks will go "Ok, Healers not super geared, but atleast I know that."