I have breakfast. You have breakfast. He/She/ it has breakfast. you have breakfast. We have breakfast. They have breakfast. Notice that "has" is only used with "He", "she" and "it".

'Has' is the present simple form of 'have' for the third person singular (she/he/it): "She has breakfast." However, there are many cases where the verb following she/he/it is in the base form ('have'). Here are some examples with auxiliary and modal verbs which are always followed by the base form: Questions: Does she have breakfast? Did she have breakfast? Will she have breakfast? Can she have breakfast? Statements with modal verbs: She should have breakfast. She might have breakfast. Negatives: She doesn't have breakfast. She didn't have breakfast. She couldn't have breakfast. She won't have breakfast. Emphatic statements She did have breakfast! 'Have' is also the subjunctive form. For example, in more formal contexts you might see this: It is important that she have breakfast. I hope that helps.

I agree with all of the above. You can also say She has had breakfast. Or She had breakfast. If you are using the past tense.

The family usually have breakfast together during the week but on weekends every one has their own break fast. I ha ve not understood use of have differetly at both the places

I didn't have something for breakfast.