''Bad energy''?

But what about friendship, good luck, succes, and money spells? Can they do harm? ( I can't really get my hands on equipment, maybe some candles tops but not more.. :()

Try doing a tarot reading before you do your spells so you can see whether the outcome is positive or not. This way, you won't be thinking so negatively whilst you perform the spell and you'll know that the 'white magick' your performing, isn't going to turn 'grey' and release bad energy.

In a way your mother is correct although its not " bad" energy but any place where magic is repeatedly practiced will tend to accumulate energy and eventually create a node

What is a node?

A area where magic is accumulated

Well in greater detail its a focal point of a large gathering of magic usually a ritual site or the home of a strong caster

It's worth noting, in my view, that certain magicks, particularly for self gain, ask for some sort of 'payment' afterwards. You might consider performing your works after an offering, so you're not left 'in debt'. I did a money spell, and immediately afterwards was more broke than usual, but things panned out well enough. Yes, make offerings, to show your commitment, gratitude and appreciation in the beginning :)

Thanks! But I don't fully understand the offerings. How can you make one in advance?

When one casts spells in a certain area repeatedly it does begin to accumulate energy as is said above, but in contrast to what is said above I would have to say protection doesn't need many materials and can very easily be done. Even with little or no energy to/through you. One can visualize a sphere around the home grounded in the natural energies of the Earth, and doing so repeatedly can give it a sort of 'permanence' over time. Now as to 'sacrifices' these can be made to any deity especially those who are over your specific task. If you do not practice religiously you can set food out or crystals in the wild as payment and state that is such.

Um, it's crap?

I find it very noble of you, in performing rituals to benefit other people (I do the same).
However, there are exceptions. Such as performing a "love" ritual, in hopes of bringing two people together, who would never given each other "the time of day".

To be in danger of this "bad energy" (as you call it), I believe you would have a curse or hex, placed upon you.

You should never tell anyone, about your practices. Unless, of course, they're a practitioner as well.
Though in such cases, as in Voodoo, it's a big "no-no" to reveal any ritual(s) you've done.
Mostly, you'll be pissing off the spirits, who'll then end the "outcome".
There are places, which consider voodoo as a weapon under the law, and you can be arrested.

-

Keep doing, what you do ...

Noble intentions always wins out.