Hi, Really sorry for your loss. Sit at least three or four rows back and then just stand/sit/kneel when everyone else does. When it's time for communion, you shouldn't go up. You also don't have to kneel. You can just sit back in the pew and no one will care either way. It's a time for quiet reflection and people certainly understand at a funeral that there will be non-Catholics and non-practising Catholics there. No one will find it strange. There may not even be communion; depends on what sort of ceremony the family has elected. (But, probably there will be.)
If prayers are recited, or songs are sung that you do not know, it's fine just to stay quiet. Again, no one will care or notice.
Usually you would turn to the person either side of you and shake hands when the Priest says, "now let us offer a sign of Peace." You don't need to kiss or embrace. Just be sure to turn to both sides, and don't be surprised if the people in front of you turn around to shake your hand, too. YOu can do the same for the people behind you, if you want to (you don't have to).
They may read out the "prayers of the faithful," to which the proper response is usually "Lord, hear our prayer." But some churches have other responses that they use. Just follow along... by the second prayer you'll know what to say. Or say nothing, that is fine, too.
Really, just focus on your friend and take the time and space you need to grieve. That's what the service is for.
Again, sorry for your loss.