Moed Katan, Chapter 1, Mishnah 10:
"Osin ma'akeh la'gag v'lamirpeset, ma'aseh hedyot aval lo ma'aseh uman" - one may build a guardrail during Chol HaMoed. A ma'akeh is the fence built at the edge of a roof or any elevated place, and the Torah requires a partition of at least ten tefachim to prevent someone from falling. The permission applies only to ma'aseh hedyot, amateur work rather than professional work: for example, he may set stones there without packing mortar between them to hold them in place, like a temporary structure. Ma'aseh uman, professional work, is forbidden.
"Shafin es hasdakin" - one may smooth over the cracks in the roof, so that water will not drip through into the house.
"U'megalgelan b'maglev, b'yad u'v'regel, aval lo b'machlatzayim" - on a flat roof that was coated with a layer of mud or cement, one may smooth it with a maglev, and likewise with the hand or the foot. But not with machlatzayim, the special tool that builders use to smooth the edge.
The Gemara raises a difficulty with the wording of the Mishnah: if it has already stated that one may use a maglev, why does the Mishnah go on to permit using the hand and the foot? The hand and the foot are certainly a less professional and less formal method than the maglev.
The Gemara explains the Mishnah's intent: in truth there is no permission to use the maglev itself, since the maglev is a professional tool, a sort of press, and in this regard its law is like that of the machlatzayim, which one has no permission to use. The Mishnah means that one may use the hand or the foot in a manner similar to rolling with a maglev.
"Hatzir v'hatzinor v'hakorah v'haman'ul v'hamafteach shenishberu - metaknan ba'mo'ed":
Hatzir - the protruding part of the door that holds the pin.
Hatzinor - the socket into which the pin enters.
Hakorah - the beam above the door.
Haman'ul - the handle with which one opens and closes the door.
Hamafteach - the key itself.
If any one of these parts broke during Chol HaMoed, one may repair it on the festival, because this is a case of loss that would cause real damage, for a person cannot leave his doors open and unlocked.
"U'bilvad shelo yechaven melachto ba'mo'ed" - the condition is that he not arrange from the outset for this work to be done during Chol HaMoed. In other words, if something broke and he wishes to repair it, and he says: I will have free time during Chol HaMoed and I will do it then - that is forbidden.
"V'chol kevashin shehu yachol le'echol mehen ba'mo'ed - kovshan" - anything that he wishes to pickle and will be able to eat from during Chol HaMoed, he is permitted to pickle, since this is a need of the festival. But if the pickling is intended for a later time, it is not permitted.