The 245th prohibition is that we are forbidden from committing robbery, i.e. taking something which isn't ours by open force and violence.

The source of this prohibition is G‑d's statement1 (exalted be He), "Lo sigzol" ["You may not commit robbery"] — as explained in the Oral Tradition,2 "The phrase 'Lo sigzol' is similar to 'Vayigzol [and he forcibly grabbed] the spear from the Egyptian's hand.' "3

This prohibition is a lav she'nitak l'aseh (a prohibition with a remedial positive commandment), i.e. the verse,4 "He must return the article that he stole." However, even if he nullified the positive commandment,5 he still does not receive lashes [unlike the regular lav she'nitak l'aseh] because a person cannot be penalized both by repayment and lashes.

[He must anyway repay] because it is a lav shenitan l'tashlumin (a prohibition that can be repaid): if he burned the object or threw it into the sea, he must pay back the value. If he denied stealing the object and swore falsely to that effect, he must pay back an additional fifth6 and bring a guilt-offering, as explained in the proper place.7 This is also explained in the end of tractate Makkos.8

The details of this mitzvah are explained in the 9th and 10th chapters of tractate Bava Kama.