A Base for a Mukteh Item
2. [The following law applies to a situation in which] at the onset of Shabbos, a non-muktzeh item was resting, [along with a muktzeh item, on top of, or inside another non-muktzeh item,] which would thus be considered a base for both a forbidden and permitted object. If one considers the permitted article more important (1), the base may be handled on Shabbos. If, however, one considers the forbidden article more important, the base may not be handled.
Therefore, it is preferable to place the challos ("loaves of bread") (2) on the table before "bein hash'moshos" ("twilight") (3), so that the table and the tablecloth will be considered a base to both the candles (which are muktzeh) and the challos (non-muktzeh) and thus, will be permitted to be moved on Shabbos (4). Otherwise, the table and the tablecloth become a base for a forbidden article alone, and hence, may not be moved (5).
Nevertheless, after the fact (that is, if only candles were left on the table at twilight), if there is a great necessity, for instance, a candle fell on the tablecloth and one had to shake it off, one may [do so], relying on [a more lenient opinion]. [This view maintains that] an article does not become a base for a muktzeh item, unless one intended that the muktzeh item remain on top of it for the entire Shabbos. Since it is customary to have a Gentile remove the candelabra on Shabbos morning, [the table] is not considered a base (6).
(1) Or equally important (See Mishna Berura 310:33). Importance is determined by the monetary value of the objects; however, if the non-muktzeh item is needed on Shabbos, it is considered "more important" even though it is of lesser value. For example, if there is an expensive calculator (muktzeh) in a drawer together with one's only challah cover, one may pull out the drawer in order to get the cover, even though it is worth less than the calculator.
(2) Or silverware and dishes.
(3) This refers to the period between sunset and the appearance of three stars, during which we refrain from doing activities which are prohibited on Shabbos, due to our inability to determine the precise moment that "night" (and therefore, shabbos), begins.
(4) The table may be moved, either for the purpose of using it in a different place, or because one wants to use the space it occupies. However, if possible, one should shake the muktzeh item off the base (if it won't be damaged), rather than carry the base along with the muktzeh item (Mishna Berura 310:34). According to most opinions, the table may be moved even if the challos are no longer on it (See MB 377:18)
(5) This is obviously only applicable to those who customarily place the Shabbos candles on the dinner table.
(6) See Shulchan Aruch 309:4 and Biur Halacha; note also Shulchon Oruch HoRav 309:9, which states that, regardless, the tablecloth is not considered a base for the candelabra.