How did slavery differ from indentured servitude?

Semantics.

There's often differences in how the people can be treated. However, the two most salient differences have to do with the permanence of the institution. Indentured servitude usually existed for a set period of time. Servants were often paying back some sort of debt which had been incurred and they were expected to work a set period of time to repay it. After that period they were free to go. In some cases, indentured servants were even given payment, in cash or land, once they completed their term of service. Slavery was usually considered permanent (at least as the defacto state. People could find ways to get themselves manumitted). The other difference was heritability. In the Atlantic slave system (which is what you're probably asking about), slavery was inherited from the mother. A child born to an enslaved woman was a slave themselves. That wasn't the case with indentured servants. Their servitude extended only to themselves and children which they had would be considered free.

Lots. 'Modern' slavery, 1500 on was of only one race, and racial slavery. The black slaves were not counted as human, only human like. They were considered property rather than people and treated and owned as animals. The indentured servants could be of any other race, from the poor and down trodden of their societies, who had to sell themselves to pay their debts or their family debts to the rich, or to the courts. They sold only their labor/ obedience and that of their children for a limited period of time, and had 2nd class citizen rights.

The black slaves had no rights at all and they their children etc. were to remain slaves forever.

Indentured servants were indentured for a fixed term, and once they had served their term they were free. Wheras slaves were slaves for life, unless their owner chose to free them. Another very important difference is that the majority of indentured servants were voluntary, whereas slaves in general were involuntary, they had not chosen to become slaves.

Indentured servitude has an ending - either the debt is paid off by the work done, or the time limit is up.

It is was a contract that it was only for a shorter time being

Basically slavery is for life while indentured servitude is for a fixed length of time. An indentured servant or indentured laborer is an employee (indenturee) within a system of unfree labor who is bound by a signed or forced contract (indenture) to work for a particular employer for a fixed time. In British North America this was typically 5 or 7 years. The contract often lets the employer sell the labor of an indenturee to a third party. Indenturees usually enter into an indenture for a specific payment or other benefit, or to meet a legal obligation, such as debt bondage. On completion of the contract, indentured servants were given their freedom, and occasionally plots of land.

Indentured servitude meant you own a person's labor. Slavery meant you owned the person.

Indentured servitude had a time limit, 5 years, 7 years, 10 years, depending on the contract.

Slavery was for life or you could be released only at the whim of your owner, which seldom happened.