As someone who work with new recruits, we are not excepting stellar contributions from day one. We are more looking for people who are willing to learn and grow, and start contributing steadily in a few weeks or months.

As a rule of thumb anyway, if you are new, you are not going to be in charge of a critical piece of the infrastructure for years to come. Likely you'll be giving relatively straightforward tasks, and once you'll have proven to be reliable you'll be given harder and more challenging tasks.

It depends on the place, but I would say that 80% of software development is rather mundane and "easy". And for the time being the harder decision will be taken by more senior people. So actually, starting is pretty comfortable and easy most of the time.

One piece of advice, do not hesitate to ask questions. We expect people to have generic CS knowledge, but it is often not enough to understand 20 years old spaghetti code. The worst recruits are the one that are too paralyzed to ask any question, and as a result you have to spend twice as long to train them because you have to guess what's wrong first.

Personally, I don't mind answering question or mentoring new people, I see it as a form of investment. Sure I am "wasting" a few hour today, but your contribution will save me countless hours in a few weeks.