Does this help? "In" implies being inside. For example, I was in the pool at XYZ Recreation Center. I believe you can usually substitute the word "in" with "inside". So in your original sentence you would NOT say "I was inside home all weekend". Therefore, you would not use "in"

Technically, 'at' is the default word for specifying locations. Situations where 'at' cannot be used (for example, with countries) are irregularities. 'In' is only used when you're inside something. Here is something I wrote in another topic: 'At' just describes where something is located. It includes most of the other prepositions. The other prepositions are used either to be more exact or because they're more natural. If in doubt, it's usually safe to use 'at'. Note that 'at' treats location like a single point in space. If the location takes up a large amount of space (like a country), thean at may be inappropriate. 'In' describes when something is inside something else. In other words, it's used when something is inside an area (2D) or volume (3D). It's usually used with buildings and rooms, as well as places that have a border (such as cities, states and countries). 'On' is used when something is attached to the surface of something else. It can also imply that something is attached or sticking to something. It'll be clear when you read some examples. Examples: -If I'm on a building, I'm standing on the roof (or climbing the walls!). If I'm in a building, I've walked in the door and am in a room. -If I'm on a planet, I'm standing on the planet. If I'm in a planet, I'm deep underground! -A clock is on a wall. Termites live in the wall. -Grass grows on the ground. Ants live in the ground. -A show is on television (imagine it attached like a poster). Wires are in the TV. In all the examples above, 'at' can technically be used (although you could argue otherwise about the TV show). However, it isn't always natural. It's usually best to use 'at' when none of the other prepositions apply. I know this doesn't help, but you just need experience to know when 'at' is natural. http://www.italki.com/question/215549

because in Spanish you have masculine and feminine gender for all nouns

This is a difficult question. I am not sure I can give a correct answer, but here are some examples of correct english that may help. "I was at home all weekend." "I was at my house all weekend." "I was in the house all weekend." "I was at the park." "I was at Ramsay Park" "I was in Ramsay Park." "I was on the grass." All of these are correct. "I was in home." "I was at the grass." "I was in the grass." These are incorrect. (The last two are not actually incorrect, but have different meanings and wouldn't make sense if you were trying to describe your location."