Sebep and neden are both noun, which means cause or reason. So we can use them as a noun in the sentence.
But neden/sebep has a usage as conjunction (bu nedenle or bu sebeple), and dolayı as conjuntion or postposition (-den dolayı). For example:
Hastayım. Bu nedenle/bu sebeple evde kaldım. (I'm sick, so/that's why I stayed at home.)
Hasta olduğumdan dolayı evde kaldım. (Because of the fact that I'm sick, I stayed at home.)
Hastalıktan dolayı evde kaldım. (Because of the sickness I stayed at home.)
But the usage of -den dolayı is a bit difficult, because the sentence or the noun before -den dolayı takes declination suffixes. So for the begining its better to use bu nedenle/bu sebeple.