A lot of DRG is about finding what your class/build is good at and doing more of that. For example, I almost exclusively play Scout, and one thing I struggle at is swarmers. There are some Scout weapons that cope a bit better with swarmers, but often the best thing I can do is flee in the direction of one of my teammates (probably the driller), and inform them I’m bringing them a gift.

A large part of learning the game is about noticing opportunities like that, especially because there aren’t hard and fast rules; it depends on your playstyle and the teams you play with. However, I will say that in the teams I play, engineers often have the highest kill count, so the issue you describe is likely just you finding your footing with the class

Most of the engineer’s kills come from their turrets. In a way, they’re more your primary than your primary. You want to place them where they have a good line of sight. Keep an eye on the indicator on the right of your screen and refill or recall them if they’re running low on ammo. If you break through into a new room, you can set them up near the entry and use them as a fallback location if things get too hot. Occasionally ask yourself “do I know where my turrets are, and are they useful there?” Keeping an eye on the ammo levels are also good for checking whether your turrets are actually shooting at anything, or whether they’re poorly placed.

Another thing to bear in mind wrt “right tool for the job” mentality is that as engineer, it can be easy to accidentally waste time and platforms building platform stairs up to high up minerals that would be best left for the scout. Platform any high up minerals and move on. Mining low down minerals is fine, and frees up the scout for getting more of those high up spots that others can’t reach. Just remember that a huge part of this game is the synergy between the classes. It can be helpful to switch up the classes every so often to begin to understand what kind of niche the others fulfill. Engineer platforms are good for building short stairs to get out of a small pit, or for covering up holes in the ground in a point defence, or for building a partial bridge over a chasm that’s too large to jump over without help.

Oh, and one last thing about engineer is that their starting secondary weapon is rarely used (at least in the people I play with). It’s not that it’s bad, it’s just that the others are pretty cool. There are assignments to unlock additional weapons. Now that I think of it, I’m not that keen on the engineer’s starting primary either. The takeaway here is that the different weapons change a lot about how a class feels, so trying other weapons can help. Regardless, most of your kills will probably come from turrets.