the different ways a person became a slave and freedom rules

A man who was very poor could sell himself. Lev. 25:39, 47
A father could sell his daughter. Ex. 21:7; Neh. 5:5
An adult woman could sell herself. Deut. 15:12-13
A thief paid off his debt by serving as a slave. Exodus 22:1-3
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It is important to note that scripture is providing guidelines for handling these situations and is not requiring these individuals to sell themselves, or saying that someone must be sold. In ancient Israel, very poor people sold themselves as servants or slaves to wealthy families in order to survive. God did not want poverty in the land. This was an ancient form of welfare. This is the background to the situations above.

However, there shall be no poor among you, since the LORD will surely bless you in the land which the LORD your God is giving you as an inheritance to possess . . . (NASB) Deut. 15:4

Freedom. The Old Testament also gave the rules for releasing slaves – giving them their freedom:

Freedom From Slavery Passage
Hebrew slaves were given their freedom after six years. Ex. 21:2
Slaves could choose to stay with their masters. Ex. 21:5-6; Deut. 15:16-17
If the slave left his master, he could take his family with him - unless he met his wife while he was with the employer. Ex. 21:3-4
Female slaves were to be freed if mistreated in anyway - especially sexual mistreatment. Ex. 21:8-11
Any slave must be freed if his or her eye or tooth were damaged. Ex. 21:26-27
Slaves could gain their freedom if family members paid for their freedom. Lev 25:48-49
Slaves could redeem themselves. Lev. 25:49
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When the year of Jubilee arrived, Hebrew slaves were to be freed. The person could have been a slave for only a short time or for six years; but when the year of Jubilee came, they were free men and women. In fact, the book of Deuteronomy requires that fellow Israelites who were slaves were to be released without regret. They were to be released and liberally given gifts from the master's flock, food and wine (Deut. 15:12-18).

It shall not seem hard to you when you set him free, for he has given you six years with double the service of a hired man; so the LORD your God will bless you in whatever you do. (NASB) Deut. 15:18