I learned way too late about the fertility cycle of my female reproductive organs. What, I can feel my cervix, if I just reach into my vagina deep enough?! And oh, so during my fertile days, my vulva will get slippery, my cervix is soft like my earlobe, and my cervical mucus becomes stretchy like egg white?! Also, my body temperature rises?! And on the not-so-fertile days, my cervix is closed, feels harder (like the tip of my nose), and none or less mucus. That's wild, so much to learn about a body that I thought I knew!
(You can use these observations to contracept or to become pregnant, but if you do, please inform yourself about Natural Family Planning (NFP) or the sympto-thermal method. It takes a routine and some experience for it to be reliable, but once you get the hang of it, it is awesome!)
Well, in German we say "bitte" or "gern geschehen", which is close to the "welcome". Of course, people can and do also say "kein Problem". I guess in my experience it depends on how I feel about the task and the person I did it for.