Preparing a fire before Shabbos comes in
The previous chapters dealt with the laws regarding leaving food on a fire from before Shabbos. The following chapter will deal with the laws of how the fire has to be lit before Shabbos in order for it to be allowed to be left on when Shabbos begins. Here too the Sages were worried that by certain types of flames there is chance that one may come to stoke them on Shabbos, and they therefore gave restrictions as to how one is allowed to leave a flame into Shabbos.
Lighting wood before Shabbos: It is forbidden to make a bonfire from wood close to Shabbos, unless one ignites the fire to such an extent that the flame burns on its own accord, without needing the help of other woods.
The reason for this restriction is because of a decree that [if this were to be allowed without restriction then] one may come to stoke it on Shabbos and move the woods in order to make the fire burn properly.
Lighting a single piece of wood before Shabbos: If one [is lighting] a single piece of wood [such as a log], then the fire needs to catch on from before Shabbos to majority of the circumference and majority of the thickness [of the wood]. Meaning that [in its inside] the fire needs to penetrate [at least] the majority of thickness of the wood, and by its outside the fire needs to encompass [at least] the majority of the woods circumference, as in such a case it will burn on its own on Shabbos without needing to move it at all.
Wood that was not lit to the above extent before Shabbos, but managed to do so on Shabbos: Wood which was not lit from before Shabbos to the extent [required, as] explained above, then even if it lit [to the required extent] on its own on Shabbos in a way that we are no longer worried that one may come to stoke it, nevertheless it is forbidden to derive benefit from it on Shabbos, since it was lit from before Shabbos in a prohibited way.
With which materials may the bon fire be made? However if the bonfire was lit from before Shabbos, to the extent required, as explained, then one may heat [his body] opposite it, and use its light. [This applies] whether it is lit on the ground or on a candelabra, and even [if its lit] from materials that are forbidden [on Shabbos] to use as a wick for a candle being that the fire sparkles on such wicks and does not catch on to the wick well, as will be explained in chapter 264. [The reason], it is permitted to use these wicks to make a bonfire in all scenarios, is because [since] a bonfire is a large fire each wick lights the other one, [and thus the fire catches on well even to wicks which are not good to be used for a candle].
Lighting coals before Shabbos: There are those which say that by coals even if the fire only caught on to a minute part of it before Shabbos, then [nevertheless] it is permitted [to leave on for Shabbos] because [the coals] light and spread on their own [once they have a fire attached to them]. However there are opinions which argue on this [and require that there be a certain amount lit to the coal before Shabbos].
The final Ruling: By a Rabbinical prohibition we rule like the lenient [first] opinion.
Lighting a bonfire with tar, sulfur, and straw before Shabbos: A bonfire of tar or of sulfur or of straw and twigs, even if the fire only caught on to them a minute amount [before Shabbos], [nevertheless] it is permitted [to be left over on Shabbos] being that they burn and spread by themselves.
Lighting a bonfire with canes and date seeds: Similarly a bonfire made from cane and of seeds of dates, when they are spread out [they too are permitted to be left over for Shabbos even if only a minute amount of them ignited before Shabbos]. However if the canes are bound together and the seeds are in a basket, then one needs to ignite the fire on to them to the point that the fire [is stabilized and] lights on its own, being that the flame will not spread to them on its own [without one actively doing so].
 Certain wicks are forbidden to be used to light candles with before Shabbos as these wicks do not burn well. Thus the Alter Rebbe here explains that there is no restrictions by a bon fire.